SIPSorcery

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

TurnServer.ReceiveUdpAsync places its generic catch (Exception) OUTSIDE the while receive loop, and Start() launches the loop fire-and-forget with no supervision or restart. A single pre-authentication UDP datagram whose STUN header first byte is in 0x80–0xFF causes STUNHeader.ParseSTUNHeader to throw ApplicationException, which unwinds past the loop and terminates it. The TURN UDP relay is then dead for ALL clients until the process is restarted.

Root Cause

src/SIPSorcery/net/TURN/TurnServer.cs:

• ReceiveUdpAsync (:555-577): the inner try (:562-567) wraps only _udpSocket.ReceiveAsync(); HandleUdpDatagram(result.Buffer, result.RemoteEndPoint) (:569) is inside the while body but OUTSIDE that inner try. The generic catch (Exception ex) (:573) is lexically OUTSIDE the while.
• Start() does _ = ReceiveUdpAsync(); (:381) — fire-and-forget, no restart.
• HandleUdpDatagram (:579) calls STUNMessage.ParseSTUNMessage(data, data.Length) (:600) for any non-ChannelData datagram; ParseSTUNMessage (STUNMessage.cs:94) has no try/catch.

Impact

ApplicationException propagates out of the while, is caught at :573, logged, and the method returns. _running remains true but nothing re-invokes ReceiveUdpAsync → TURN UDP relay permanently unavailable for all clients (whole-server DoS). Pre-authentication: STUN parsing precedes any TURN allocation/credential check.

Proof of Concept

Send one UDP datagram to the TURN port (default 3478) with first byte 0x80 (e.g. 80 00 00 00). 0x80 & 0xC0 = 0x80 ≠ 0x40 → not ChannelData → ParseSTUNMessage → ParseSTUNHeader executes if ((Array[startIndex] & 0xC0) != 0) throw new ApplicationException(...) (STUNHeader.cs:169-172); 0x80 & 0xC0 = 0x80 ≠ 0 → throws.

Attack Chain

1. Entry: one UDP datagram to the TURN port, first byte 0x80–0xFF. Guard: ChannelData branch requires (data[0] & 0xC0) == 0x40 (:583). Bypass: 0x80 & 0xC0 = 0x80 ≠ 0x40 → falls through to ParseSTUNMessage (:600).
2. Sink: STUNMessage.ParseSTUNMessage → STUNHeader.ParseSTUNHeader (STUNHeader.cs:169-172) throws ApplicationException. Guard: none before the throw; ParseSTUNMessage has no try/catch. Bypass: 0x80 & 0xC0 = 0x80 ≠ 0 → throws.
3. Impact: exception unwinds past the while into catch(Exception) at :573 → logged → method returns → loop exits. Guard: none — no restart (Start() :381 fire-and-forget). Bypass: N/A. TURN UDP relay dead for all clients until process restart.

Bypass Evidence

• Loop/catch structure: catch at TurnServer.cs:573 is outside the while at :559; HandleUdpDatagram at :569 is outside the inner try (:562-567).
• Unguarded ParseSTUNMessage at :600; throw at STUNHeader.cs:169-172.
• Fire-and-forget start at :381 with no restart in Start().
• TurnServerConfig.ListenAddress defaults to IPAddress.Loopback (:42), but a functioning TURN server must bind a routable address to serve clients, so real deployments are exposed. Non-default config narrows the vulnerable population, not the attack difficulty → AC:L.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (TurnServer component present since 10.0.5; verified on release tag v10.0.13 and HEAD).

Dedup

NOT a duplicate of GHSA-28gm-jrmw-xx93 (CVE-2026-54632), which covers the client RTP/ICE socket (UdpReceiver/RTPChannel). TurnServer is a distinct shipped RFC 5766 server component with its own loop and fix location.

Suggested Fix

Wrap HandleUdpDatagram in a per-datagram try/log-and-continue INSIDE the while (matching the drop-and-continue intent of fix bdb76cb), and/or add loop supervision/restart.

Reported by zx (Jace) — GitHub: @manus-use

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use

Impact

A single malformed inbound UDP packet on the RTP/ICE socket can remotely terminate an active RTP or WebRTC media session. The packet receive handler indexes packet (and STUN attribute) bytes without sufficient length checks and throws, and the UDP receive loop converted any such exception into a channel Close rather than dropping the packet. One small, unauthenticated packet therefore ends the media session.

This is reachable during ICE connectivity checks — before the DTLS handshake and before any STUN MESSAGE-INTEGRITY verification. Because the RTP/ICE port is shared/advertised in the ICE candidates, a peer or on-path attacker can reach it (exposure is lower for a blind off-path attacker that must first learn the ephemeral port). Impact is availability only — no loss of confidentiality or integrity.

Affected versions

NuGet package SIPSorcery <= 10.0.8.

Patches

Fixed in 10.0.9.

Root cause

Two issues combine:

1. Unchecked indexing of untrusted bytes.

   • RTPChannel.OnRTPPacketReceived read packet[1] after only checking the packet was non-empty, so a 1-byte packet threw IndexOutOfRangeException.
   • STUNAttribute.ParseMessageAttributes passed a null/short value to the typed attribute parsers, and STUNXORAddressAttribute (and the non-XOR STUNAddressAttribute) then read attributeValue[1], AsSpan(2) and AsSpan(4) with no length check. A STUN message carrying an XOR-MAPPED-ADDRESS, XOR-PEER-ADDRESS or XOR-RELAYED-ADDRESS attribute of length 0–7 threw (NullReferenceException for length 0, IndexOutOfRangeException/ArgumentOutOfRangeException for 1–7).

2. The UDP receive loop closed the channel on any exception. The catch-all in UdpReceiver.EndReceiveFrom called Close(), tearing down the channel, instead of dropping the offending packet and continuing. This was systemic: any unhandled exception anywhere in the packet pipeline (STUN, RTP, RTCP, DTLS demux, SRTP, TURN) became a channel teardown.

Fix

• UdpReceiver.EndReceiveFrom: a non-socket exception now logs and drops the single packet and re-arms the receive loop (matching the existing SIPUDPChannel behaviour), instead of closing the channel. Genuine socket failures continue to be handled separately.
• RTPChannel.OnRTPPacketReceived: requires a minimum packet length (RTPHeader.MIN_HEADER_LEN) before indexing the discriminator bytes.
• STUN parsing: ParseMessageAttributes validates each attribute value length and skips malformed/truncated attributes; the XOR/address attribute constructors validate length defensively; ParseSTUNMessage no longer dereferences a null attribute list.

Regression tests were added covering the 1-byte packet (channel stays open and remains usable), short/zero-length XOR address attributes (0–7 bytes), and truncated STUN messages.

Workarounds

None within the library short of upgrading. Restricting the RTP/ICE port to known peers at the network layer reduces exposure but does not eliminate it, since a negotiating peer can still trigger the condition.

Credit

Responsibly reported by Lokhesh Ujhoodha.

Summary

SctpSackChunk.ParseChunk reads the numGapAckBlocks and numDuplicateTSNs fields (each up to 65535) directly from an attacker-controlled SCTP SACK chunk and loops that many times reading 4 bytes per iteration, with no validation of the counts against the chunk length or the receive buffer. A single crafted SACK chunk from a negotiated WebRTC peer forces reads past the end of the 262144-byte receive buffer, raising IndexOutOfRangeException, which is not caught by the recoverable handler and terminates the dedicated SCTP receive thread — permanently killing the SCTP association and all data channels.

Root Cause

src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs:

• ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8); (:141)
• ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10); (:142)
• gap-ack loop (:146) and duplicate-TSN loop (:154) index the buffer via NetConvert.ParseUInt16/32 (buffer[posn], no bounds check — sys/Net/NetConvert.cs:30,41). SctpPacket.ParseChunks (SctpPacket.cs:195-203) only validates chunkLength >= 4 and posn+chunkLength <= length; the counts inside the value are never checked. RTCSctpTransport.DoReceive calls SctpPacket.Parse(recvBuffer, 0, bytesRead) on a reused recvBuffer = new byte[262144].

Impact

IndexOutOfRangeException is a SystemException, not ApplicationException, so the recoverable catch (ApplicationException) { … continue; } at RTCSctpTransport.cs:345 is skipped and control falls to the generic catch (Exception) { … break; } at :356. The break exits the receive loop, DoReceive returns, and the dedicated _receiveThread = new Thread(DoReceive) (:173, started once) exits with no restart → the SCTP association and every data channel are permanently dead (denial of service).

Proof of Concept

A negotiated WebRTC peer (post-DTLS) sends a checksum-valid SCTP packet: 12-byte common header + a SACK chunk (type 3) with chunkLength=16, numGapAckBlocks=0xFFFF, numDuplicateTSNs=0xFFFF. CRC32C is attacker-computable. The gap-ack loop reaches buffer[262144] on a 262144-byte array (valid indices 0..262143) → IndexOutOfRangeException.

Attack Chain

1. Entry: post-DTLS negotiated peer sends a checksum-valid SCTP packet with a SACK chunk (chunkLength=16, numGapAckBlocks=0xFFFF). Guard: VerifyChecksum (CRC32C). Bypass: CRC32C is computable by the sender.
2. Processing: DoReceive (RTCSctpTransport.cs:286) reads into reused recvBuffer (262144 bytes, :280) → SctpPacket.Parse(recvBuffer, 0, bytesRead) (:302) → ParseChunks → SACK dispatch (SctpChunk.Parse :340-341) → SctpSackChunk.ParseChunk. Guard: ParseChunks checks only chunkLength>=4 and posn+chunkLength<=length (SctpPacket.cs:195-203). Bypass: chunkLength=16 is well-formed; the counts are never validated.
3. Sink: gap-ack loop (SctpSackChunk.cs:146) calls NetConvert.ParseUInt16(buffer, reportPosn) with reportPosn starting at startPosn(16)+FIXED_PARAMETERS(12)=28, climbing +4 each iteration. Guard: none on the count. Bypass: NetConvert.ParseUInt16 (NetConvert.cs:30) indexes buffer[posn] unchecked.
4. Impact: at iteration 65529, reportPosn = 28 + 65529*4 = 262144 → buffer[262144] → IndexOutOfRangeException → generic catch at RTCSctpTransport.cs:356 → break → receive thread exits, no restart → association permanently dead.

Bypass Evidence

• Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.
• NetConvert.ParseUInt16 unchecked indexing (NetConvert.cs:30).
• ParseChunks validates only chunkLength (SctpPacket.cs:195-203).
• OOB math: 28 + 65535*4 = 262168 > 262144; buffer is 262144 (DEFAULT_ADVERTISED_RECEIVE_WINDOW, SctpAssociation.cs:62). numGapAckBlocks alone suffices — the dup-TSN loop is not needed.
• DoReceive catch split: recoverable catch(ApplicationException) at :345 (continue) vs generic catch(Exception) at :356 (break); _receiveThread started once at :176.

Affected Versions

nuget:SIPSorcery <= 10.0.13 (verified present on release tag v10.0.13 and HEAD da944543).

Dedup

NOT a duplicate of GHSA-qmvg-569h-hqrh — that fix (fe5a1fa) touched only SctpPacket.cs (the chunk-cursor zero-length infinite loop, CWE-835). This is a distinct out-of-bounds read (CWE-125) in SctpSackChunk count loops, untouched by that fix.

Suggested Fix

Validate startPosn + FIXED_PARAMETERS_LENGTH + numGapAckBlocks*4 + numDuplicateTSNs*4 <= posn + chunkLen before the loops, and/or make NetConvert.Parse* bounds-checked, and/or treat IndexOutOfRangeException/ArgumentException as recoverable in DoReceive.

Reported by zx (Jace) — GitHub: @manus-use