capnp

Cap'n Proto for Rust

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Activity

Latest release: 6d ago
Total releases: 207
Cadence: ~12 days
Last 12 months: 21

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Stars: 2.5k

Details

License: MIT
First release: Nov 20, 2014

Releases

Version	Released
`0.27.2` patch	Sep 08, 2026
`0.27.1` patch	Sep 04, 2026
`0.27.0` minor	Aug 02, 2026
`0.26.2` patch	Jul 05, 2026
`0.26.1` patch	Jul 02, 2026
`0.26.0` minor	Jun 17, 2026
`0.25.6` patch	Jun 16, 2026
`0.25.5` patch	Jun 01, 2026
`0.25.4` patch	Apr 12, 2026
`0.25.3` patch	Mar 30, 2026
`0.25.2` patch	Mar 12, 2026
`0.25.1` patch	Feb 12, 2026
`0.25.0` minor	Jan 09, 2026
`0.24.1` patch	Jan 08, 2026
`0.24.0` minor	Dec 24, 2025
`0.23.2` patch 1 CVE	Dec 22, 2025
`0.23.1` patch 1 CVE	Dec 16, 2025
`0.23.0` minor 1 CVE	Oct 28, 2025
`0.22.0` minor 1 CVE	Oct 27, 2025
`0.21.7` patch 1 CVE	Oct 17, 2025
`0.21.6` patch 1 CVE	Oct 11, 2025
`0.21.5` patch 1 CVE	Aug 31, 2025
`0.21.4` patch 1 CVE	Jul 25, 2025
`0.21.3` patch 1 CVE	Jul 22, 2025
`0.21.2` patch 1 CVE	Jul 02, 2025
`0.21.1` patch 1 CVE	May 26, 2025
`0.21.0` minor 1 CVE	Apr 08, 2025
`0.20.6` patch 1 CVE	Mar 07, 2025
`0.20.5` patch 1 CVE	Mar 05, 2025
`0.20.4` patch 1 CVE	Mar 02, 2025
`0.20.3` patch 1 CVE	Oct 22, 2024
`0.19.8` patch 1 CVE	Oct 15, 2024
`0.20.2` patch 1 CVE	Oct 15, 2024
`0.20.1` patch 1 CVE	Sep 23, 2024
`0.20.0` minor 1 CVE	Sep 17, 2024
`0.19.7` patch 1 CVE	Sep 09, 2024
`0.19.6` patch 1 CVE	May 28, 2024
`0.19.5` patch 1 CVE	May 16, 2024
`0.19.4` patch 1 CVE	May 13, 2024
`0.19.3` patch 1 CVE	Mar 29, 2024
`0.19.2` patch 1 CVE	Feb 19, 2024
`0.19.1` patch 1 CVE	Jan 15, 2024
`0.19.0` minor 1 CVE	Jan 14, 2024
`0.18.13` patch 1 CVE	Jan 11, 2024
`0.18.12` patch 1 CVE	Jan 11, 2024
`0.18.11` patch 1 CVE	Jan 06, 2024
`0.18.10` patch 1 CVE	Dec 10, 2023
`0.18.9` patch 1 CVE	Dec 01, 2023
`0.18.8` patch 1 CVE	Nov 30, 2023
`0.18.7` patch 1 CVE	Nov 15, 2023

1–50 of 207

Repository

capnproto/capnproto-rust

Forks: 264
Open issues: 73
Language: Rust
: 5.1/ 10

Dependencies (3)

Depends on

0.27.2

Used by

148

Supply-chain exposure

148 tracked projects depend on this, <1% of every package we track.

A known CVE here directly exposes every one of them.

Known CVEs (2)

GHSA-5w5r-mf82-595p RUSTSEC-2025-0143 Jan 28, 2026

Cap'n Proto has Undefined Behavior in constant::Reader and StructSchema

Critical
Network Low None None

The safe API functions constant::Reader::get and StructSchema::new rely on PointerReader::get_root_unchecked, which can cause undefined behavior (UB) by constructing arbitrary words or schemas.

Reader::get

pub fn get(&self) -> Result<<T as Owned>::Reader<'static>> { // ... // UNSAFE: access `words` without validation }

StructSchema::new

pub fn new(builder: RawBrandedStructSchema) -> StructSchema { // ... // UNSAFE: access encoded nodes without validation }

This vulnerability allows safe Rust code to trigger UB, which violates Rust's safety guarantees.

The issue is resolved in version 0.24.0 by making constructor functions unsafe and mark the fields of struct as visible only in the crate.

Fixed in

0.24.0

References

https://github.com/capnproto/capnproto-rust/issues/605
https://github.com/capnproto/capnproto-rust/commit/7b981f4c75a975c80444cd38729bcdf12bf3eabf
https://github.com/capnproto/capnproto-rust/commit/e3aeec213e6d1b30a182bf61682a370f20d8a02c
https://github.com/capnproto/capnproto-rust
https://rustsec.org/advisories/RUSTSEC-2025-0143.html

Updated Feb 03, 2026 · Source: OSV.dev
CVE-2022-46149 GHSA-qqff-4vw4-f6hx RUSTSEC-2022-0068 Dec 05, 2022

Cap'n Proto and its Rust implementation vulnerable to out-of-bounds read due to logic error handling list-of-list

5.4 / 10
Medium
Network High None None Changed Low None Low

The Cap'n Proto library and capnp Rust package are vulnerable to out-of-bounds read due to logic error handling list-of-list. If a message consumer expects data of type "list of pointers", and if the consumer performs certain specific actions on such data, then a message producer can cause the consumer to read out-of-bounds memory. This could trigger a process crash in the consumer, or in some cases could allow exfiltration of private in-memory data.

Impact

Remotely segfault a peer by sending it a malicious message, if the victim performs certain actions on a list-of-pointer type.

Possible exfiltration of memory, if the victim performs additional certain actions on a list-of-pointer type.

To be vulnerable, an application must perform a specific sequence of actions, described below. At present, we are not aware of any vulnerable application, but we advise updating regardless.

Fixed in

Unfortunately, the bug is present in inlined code, therefore the fix will require rebuilding dependent applications.

C++ fix:

git commit 25d34c67863fd960af34fc4f82a7ca3362ee74b9

release 0.11 (future)

release 0.10.3:

Unix: https://capnproto.org/capnproto-c++-0.10.3.tar.gz

Windows: https://capnproto.org/capnproto-c++-win32-0.10.3.zip

release 0.9.2:

Unix: https://capnproto.org/capnproto-c++-0.9.2.tar.gz

Windows: https://capnproto.org/capnproto-c++-win32-0.9.2.zip

release 0.8.1:

Unix: https://capnproto.org/capnproto-c++-0.8.1.tar.gz

Windows: https://capnproto.org/capnproto-c++-win32-0.8.1.zip

release 0.7.1:

Unix: https://capnproto.org/capnproto-c++-0.7.1.tar.gz

Windows: https://capnproto.org/capnproto-c++-win32-0.7.1.zip

release 0.5.4:

Unix: https://capnproto.org/capnproto-c++-0.5.4.tar.gz

Windows: https://capnproto.org/capnproto-c++-win32-0.5.4.zip

Rust fix:

capnp crate version 0.15.2, 0.14.11, or 0.13.7

Details

A specially-crafted pointer could escape bounds checking by exploiting inconsistent handling of pointers when a list-of-structs is downgraded to a list-of-pointers.

For an in-depth explanation of how this bug works, see David Renshaw's blog post. This details below focus only on determining whether an application is vulnerable.

In order to be vulnerable, an application must have certain properties.

First, the application must accept messages with a schema in which a field has list-of-pointer type. This includes List(Text), List(Data), List(List(T)), or List(C) where C is an interface type. In the following discussion, we will assume this field is named foo.

Second, the application must accept a message of this schema from a malicious source, where the attacker can maliciously encode the pointer representing the field foo.

Third, the application must call getFoo() to obtain a List<T>::Reader for the field, and then use it in one of the following two ways:

Pass it as the parameter to another message's setFoo(), thus copying the field into a new message. Note that copying the parent struct as a whole will not trigger the bug; the bug only occurs if the specific field foo is get/set on its own.

Convert it into AnyList::Reader, and then attempt to access it through that. This is much less likely; very few apps use the AnyList API.

The dynamic API equivalents of these actions (capnp/dynamic.h) are also affected.

If the application does these steps, the attacker may be able to cause the Cap'n Proto implementation to read beyond the end of the message. This could induce a segmentation fault. Or, worse, data that happened to be in memory immediately after the message might be returned as if it were part of the message. In the latter case, if the application then forwards that data back to the attacker or sends it to another third party, this could result in exfiltration of secrets.

Any exfiltration of data would have the following limitations:

The attacker could exfiltrate no more than 512 KiB of memory immediately following the message buffer.

The attacker chooses in advance how far past the end of the message to read.

The attacker's message itself must be larger than the exfiltrated data. Note that a sufficiently large message buffer will likely be allocated using mmap() in which case the attack will likely segfault.

The attack can only work if the 8 bytes immediately following the exfiltrated data contains a valid in-bounds Cap'n Proto pointer. The easiest way to achieve this is if the pointer is null, i.e. 8 bytes of zero.

The attacker must specify exactly how much data to exfiltrate, so must guess exactly where such a valid pointer will exist.

If the exfiltrated data is not followed by a valid pointer, the attack will throw an exception. If an application has chosen to ignore exceptions (e.g. by compiling with -fno-exceptions and not registering an alternative exception callback) then the attack may be able to proceed anyway.

Fixed in

0.13.70.14.110.15.2

References

https://github.com/capnproto/capnproto/security/advisories/GHSA-qqff-4vw4-f6hx
https://nvd.nist.gov/vuln/detail/CVE-2022-46149
https://github.com/capnproto/capnproto/commit/25d34c67863fd960af34fc4f82a7ca3362ee74b9
https://dwrensha.github.io/capnproto-rust/2022/11/30/out_of_bounds_memory_access_bug.html
https://github.com/capnproto/capnproto
https://github.com/capnproto/capnproto/tree/master/security-advisories/2022-11-30-0-pointer-list-bounds.md

Updated Nov 08, 2023 · Source: OSV.dev

Insights

Releases per month

last 12 months

Release mix

minor 27
patch 179

207 releases

Dependencies over time

per release

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