GHSA-jwjp-4649-v8jp: SIPSorcery Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jwjp-4649-v8jp",
  "modified" : "2026-08-12T19:30:43Z",
  "published" : "2026-08-12T19:30:43Z",
  "aliases" : [ ],
  "summary" : "SIPSorcery vulnerable to Denial of Service via out-of-bounds read in SCTP SACK chunk parsing",
  "details" : "## Summary\n`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.\n\n## Root Cause\n`src/SIPSorcery/net/SCTP/Chunks/SctpSackChunk.cs`:\n- `ushort numGapAckBlocks = NetConvert.ParseUInt16(buffer, startPosn + 8);` (:141)\n- `ushort numDuplicateTSNs = NetConvert.ParseUInt16(buffer, startPosn + 10);` (:142)\n- 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`).\n`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]`.\n\n## Impact\n`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).\n\n## Proof of Concept\nA 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`.\n\n## Attack Chain\n1. 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.\n2. 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.\n3. 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.\n4. 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.\n\n## Bypass Evidence\n- Unchecked counts at SctpSackChunk.cs:141-142; loops at :146,:154.\n- `NetConvert.ParseUInt16` unchecked indexing (NetConvert.cs:30).\n- `ParseChunks` validates only `chunkLength` (SctpPacket.cs:195-203).\n- 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.\n- `DoReceive` catch split: recoverable `catch(ApplicationException)` at :345 (`continue`) vs generic `catch(Exception)` at :356 (`break`); `_receiveThread` started once at :176.\n\n## Affected Versions\n`nuget:SIPSorcery <= 10.0.13` (verified present on release tag v10.0.13 and HEAD da944543).\n\n## Dedup\nNOT 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.\n\n## Suggested Fix\nValidate `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`.\n\n---\nReported by **zx (Jace)** — GitHub: @manus-use",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "SIPSorcery"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "10.0.14"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 10.0.13"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sipsorcery-org/sipsorcery/security/advisories/GHSA-jwjp-4649-v8jp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sipsorcery-org/sipsorcery/commit/a2466550bb2a28821c73fb1961bc33dcc467f8cf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sipsorcery-org/sipsorcery"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-125", "CWE-755" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-12T19:30:43Z",
    "nvd_published_at" : null
  }
}