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CVE-2026-23457 Linux CVE debrief

A vulnerability in the Linux kernel's netfilter SIP connection tracking module (nf_conntrack_sip) allows an attacker to trigger incorrect message boundary parsing in sip_help_tcp(). The root cause is a type mismatch: simple_strtoul() returns unsigned long, but the result is stored in unsigned int clen. On 64-bit systems, Content-Length values exceeding UINT_MAX (e.g., 4294967328) are silently truncated, causing the parser to miscalculate where the current SIP message ends. The loop then incorrectly treats trailing TCP segment data as a second SIP message and processes it through the SDP parser. This can lead to unexpected state in the connection tracker and potential availability impact. The fix changes clen to unsigned long and adds validation to reject Content-Length values exceeding remaining TCP payload length.

Vendor
Linux
Product
Unknown
CVSS
HIGH 8.6
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-14
Original CVE updated
2026-07-28
Advisory published
2026-07-14
Advisory updated
2026-07-28

Who should care

Linux system administrators running VoIP/SIP services with netfilter connection tracking enabled; security teams managing kernel attack surface; network engineers responsible for SIP infrastructure availability

Technical summary

The nf_conntrack_sip module's TCP helper (sip_help_tcp()) parses SIP Content-Length headers using simple_strtoul() but stores the result in unsigned int. On 64-bit architectures, this causes truncation of values > UINT_MAX, leading to incorrect message boundary calculation. The parser then misidentifies trailing data as a separate SIP message, potentially causing connection tracking state corruption. The fix promotes clen to unsigned long and adds bounds checking against remaining payload length.

Defensive priority

high

Recommended defensive actions

  • Apply kernel patches from stable branches: 5.10.253+, 5.15.203+, 6.1.167+, 6.6.130+, 6.12.78+, 6.18.20+, 6.19.10+, or later stable versions
  • If immediate patching is not possible, consider disabling SIP connection tracking helper (nf_conntrack_sip) if not required for VoIP infrastructure
  • Monitor for kernel updates from distribution vendors for backported fixes
  • Review firewall/netfilter configurations to assess exposure of SIP services to untrusted networks

Evidence notes

CVE published 2026-04-03; NVD analyzed status with CVSS 8.6 HIGH. Multiple stable kernel patches available across affected branches. CPE criteria indicate affected versions from 2.6.34 through multiple stable branches (5.10, 5.15, 6.1, 6.6, 6.12, 6.18, 6.19) and 7.0-rc series.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-23457 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-23457

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-23457 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-23457

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/528b4509c9dfc272e2e92d811915e5211650d383

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/75fcaee5170e7dbbee778927134ef2e9568b4659

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/865dba58958c3a86786f89a501971ab0e3ec6ba9

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/b75209debb9adab287b3caa982f77788c1e15027

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/cd1b7403ec835f8a0b3f1f7e68ac26af2cb1e42f

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/d4f17256544cc37f6534a14a27a9dec3540c2015

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

  • Mitigation or vendor reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/ed81b6a7012485acdb9c6c80735a0b7d8e5e1873

    416baaa9-dc9f-4396-8d5f-8c081fb06d67 - Patch

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.