Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.

CVE-2026-40881: addr/addrv2 Deserialization Resource Exhaustion

Summary

When deserializing addr or addrv2 messages, which contain vectors of addresses, Zebra would fully deserialize them up to a maximum length (over 233,000) that was derived from the 2 MiB message size limit. This is much larger than the actual limit of 1,000 messages from the specification. Zebra would eventually check that limit but, at that point, the memory for the larger vector was already allocated. An attacker could cause out-of-memory aborts in Zebra by sending multiple such messages over different connections.

Severity

Moderate - This is a Denial of Service Vulnerability that could allow an attacker to crash a Zebra node.

Affected Versions

All Zebra versions prior to version 4.3.1.

Description

The vulnerability exists in the read_addr/addrv2 functions in codec.rs. It deserializes a vector of addresses with the zcash_deserialize() trait method, which uses as a upper bound the result of T::max_allocation(). For theses types, it was derived from dividing the max message size (2 MiB) by the minimum serialized size of one entry. For AddrV1: 2_097_152 / 30 = 69,904. For AddrV2: 2_097_152 / 9 = 233,016. Only after deserialization was the MAX_ADDRS_IN_MESSAGE = 1000 limit checked.

An attacker could exploit this by:

1. Creating addr or addrv2 messages with a large number of entries.
2. Submitting them to a Zebra node, possibly through multiple connections, to attempt to get Zebra into an out-of-memory state.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Zebra node crash.
• Scope: Any impacted Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.3.1.

The fix changes the max_allocation() method for the relevant types to return 1,000, thus blocking larger values prior to deserialization.

Mitigation

Users should upgrade to Zebra 4.3.1 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains not vulnerable to the denial of service attack.

Credits

Thanks @Zk-nd3r for finding and reporting the issue, and suggesting the fix.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node listens on the default [::] address on a Linux host (the standard deployment configuration — net.ipv6.bindv6only=0 is the default on all common Linux distributions).
3. Your node is synced near the chain tip (the expected production state for any node participating in the network).

Summary

An address normalization mismatch between the handshake path and the mempool misbehavior path causes a deterministic assertion panic when a peer connects via IPv4 to a dual-stack IPv6 listener and then triggers a mempool misbehavior penalty.

The handshake path canonicalizes IPv4-mapped IPv6 addresses to plain IPv4 when storing the peer in the address book via MetaAddr::new_connected. The mempool misbehavior path forwards the raw transient socket address (IPv4-mapped IPv6 form) when sending MetaAddrChange::UpdateMisbehavior to the address book. The address book looks up the canonical IPv4 entry but then asserts that the previous entry's address matches the change's address. The mismatch between the canonical IPv4 address and the raw IPv4-mapped IPv6 address triggers the assertion, and panic = "abort" terminates the process.

Details

On Linux with net.ipv6.bindv6only=0, an IPv4 connection accepted by a [::] listener is represented internally as an IPv4-mapped IPv6 socket address (e.g., ::ffff:127.0.0.1:8233). Zebra's canonical_peer_addr helper converts these to plain IPv4 (e.g., 127.0.0.1:8233).

The handshake path uses MetaAddr::new_connected, which canonicalizes the address before storing in the address book. However, inbound inventory registration uses connected_addr.get_transient_addr(), preserving the raw IPv4-mapped form. When the mempool later downloads an invalid transaction from this peer and generates a misbehavior penalty, the raw transient address is forwarded through the misbehavior channel to MetaAddrChange::UpdateMisbehavior, which does not canonicalize.

After the 30-second misbehavior batch flush, AddressBook::update retrieves the canonical IPv4 entry but MetaAddrChange::apply_to_meta_addr asserts that previous.addr == self.addr(), which fails because one is IPv4 and the other is IPv4-mapped IPv6.

The attacker needs only to complete a P2P handshake over IPv4 to a dual-stack listener and advertise an invalid mempool transaction (such as a coinbase transaction). The assertion fires after the 30-second misbehavior batch flush.

Patches

Patched in Zebra 4.5.0. The fix canonicalizes the address in the misbehavior update path via a new MetaAddr::new_misbehavior constructor that applies canonical_peer_addr before creating the UpdateMisbehavior change.

Workarounds

Configuring listen_addr to an IPv4-only address (e.g., 0.0.0.0:8233) avoids the IPv4-mapped IPv6 representation and prevents this specific assertion. Alternatively, setting net.ipv6.bindv6only=1 on Linux prevents dual-stack acceptance.

Impact

A remote unauthenticated peer can deterministically crash any synced Zebra node running the default Linux dual-stack configuration with a single invalid mempool transaction advertisement, followed by a 30-second wait. The attack requires no mining capability, no RPC access, no funds, and no special privileges. The crash can be repeated after each restart, causing persistent downtime. Linux dual-stack sockets and mempool activation are the default production state, not special preconditions.

Credit

Reported by @Haxatron.

Am I affected

You are affected if:

1. You run zebrad up to and including v4.4.1.
2. Your node accepts inbound P2P connections (network.listen_addr is set, which is the default).

Summary

The P2P codec's Codec::decode() method calls src.reserve(body_len + HEADER_LEN) after parsing a 24-byte protocol header, using the attacker-claimed body_len field. This reserves up to MAX_PROTOCOL_MESSAGE_LEN (~2 MiB) of virtual buffer capacity per connection before any body bytes arrive and before the handshake completes.

However, BytesMut::reserve() sets virtual capacity without committing physical memory pages. The operating system does not allocate physical RAM until bytes are actually written into the buffer. Since the attacker never sends body bytes, the reserved capacity remains uncommitted. Reproduction of the reporter's PoC (256 threads, 30 seconds of sustained connections) showed negligible RSS impact on the Zebra process.

Zebra's existing mitigations further constrain the practical attack surface: per-IP connection limits (max_connections_per_ip = 1), a per-connection accept rate of approximately one per second, and a 3-second handshake timeout that cleans up idle connections.

Details

At zebra-network/src/protocol/external/codec.rs:406, after parsing the 24-byte header and validating the network magic and body length against MAX_PROTOCOL_MESSAGE_LEN, the codec calls src.reserve(body_len + HEADER_LEN). The codec is constructed on the bare TCP stream before negotiate_version() runs, so the reservation is reachable from any TCP peer that can send 24 bytes.

No legitimate Zcash handshake message (version, verack) is anywhere close to 2 MiB. The codec makes no distinction between pre-handshake and post-handshake message types when sizing the reservation.

Patches

The fix defers large buffer reservations until after the handshake completes, or caps the per-message reservation for pre-handshake messages to what version/verack actually require.

Workarounds

No workaround is needed. The existing per-IP rate limiting, handshake timeout, and connection limits effectively mitigate the practical impact.

Impact

Minimal. The reservation affects virtual address space only, not physical memory. Zebra's existing connection-management mitigations (per-IP limits, accept rate, handshake timeout) further constrain the attack. The code path is worth cleaning up for defense-in-depth but does not produce a measurable denial-of-service effect.

Credit

Reported by @ouicate via a private GitHub Security Advisory submission.

CVE-2026-44500: Allocation Amplification in Inbound Network Deserializers

Summary

Several inbound deserialization paths in Zebra allocated buffers sized against generic transport or block-size ceilings before the tighter protocol or consensus limits were enforced. An unauthenticated or post-handshake peer could therefore force the node to preallocate and parse for orders of magnitude more data than the protocol intended, across headers messages, equihash solutions in block headers, Sapling spend vectors in V5/V4 transactions, and coinbase script bytes in blocks.

Severity

Moderate - This is a Denial-of-Service Vulnerability that could allow a malicious peer to amplify per-message memory and parse cost on Zebra nodes, with effects amplified by multi-peer fan-in.

Each individual case is bounded by the 2 MiB transport ceiling or the block-size cap, so no single message causes unbounded allocation, but the cumulative gap between intended and actual limits is significant.

Affected Versions

All Zebra versions prior to 4.4.0.

Description

Zebra's network codec uses TrustedPreallocate and generic Vec deserialization to bound inbound message parsing. In several places the bound used at the deserializer was the generic transport or block-size ceiling rather than the tighter protocol or consensus rule that applies to the field, so allocation happened first and the real limit was only enforced afterwards. Four such cases were identified:

• headers message receive cap. read_headers() deserialized the CountedHeader vector via the generic TrustedPreallocate path, which allowed up to ~1,409 entries per message. The protocol ceiling MAX_FIND_BLOCK_HEADERS_RESULTS = 160 was only used on the send side, giving an ~8.8x preallocation gap on receive. Reachable before the version handshake completes since the codec is installed on raw bytes.
• Equihash solution length. Solution::zcash_deserialize decoded the solution as a generic Vec<u8> and only checked the exact consensus size (1344 bytes mainnet/testnet, 36 bytes regtest) afterwards in Solution::from_bytes. A single fixed-size header field could be inflated to nearly the full block-size ceiling before rejection.
• Sapling spend vectors in coinbase transactions. V5 spend_prefixes and V4 shielded_spends were allocated generically with block-size-derived ceilings (~5,681 / ~5,208 entries) before the consensus rule that coinbase transactions have zero Sapling spends was enforced in the verifier.
• Coinbase script bytes. Input::zcash_deserialize() read the coinbase script as a generic Vec<u8> up to the message-size cap before enforcing the consensus rule that coinbase scripts are between 2 and 100 bytes.

An attacker could exploit this by:

• Opening an inbound TCP connection (and, for the latter three cases, completing the version handshake).
• Sending one of: a headers message with a CompactSize count up to ~1,409, a block whose header carries an inflated equihash CompactSize, a tx declaring a coinbase input with a large nSpendsSapling, or a block with a coinbase input whose script length is near the message-size ceiling.
• The deserializer allocates against the loose ceiling, parses, and only then rejects.

Impact

Denial of Service

• Attack Vector: Network.
• Effect: Amplified per-message allocation and parse cost on inbound peer messages, stackable across concurrent connections. The concrete effect will be influenced by how much memory Zebra has available.
• Scope: Any affected Zebra node.

Fixed Versions

This issue is fixed in Zebra 4.4.0.

Mitigation

Users should upgrade to Zebra 4.4.0 or later immediately.

There are no known workarounds for this issue. Immediate upgrade is the only way to remove the amplified allocation surface on inbound peer messages.

Credits

Zebra thanks @Zk-nd3r for finding and reporting the issues.