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CVE Record

CVE-2026-23457: netfilter: nf_conntrack_sip: fix Content-Length u32 truncation in sip_help_tcp()

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.

HighCVSS 8.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A remotely supplied oversized SIP Content-Length can be truncated by Linux’s netfilter SIP connection-tracking code. This can make the kernel misidentify message boundaries and process trailing network data incorrectly. The supplied CVSS score is 8.6, with availability identified as the greatest potential impact.

Executive priority

Treat this as a high-priority patching issue for systems actively processing untrusted SIP traffic, especially network infrastructure whose failure would disrupt communications. Absence from KEV and lack of cited exploitation evidence do not justify emergency-wide shutdowns, but exposed systems should enter the next expedited maintenance cycle.

Technical view

On 64-bit systems, sip_help_tcp() parsed Content-Length as unsigned long but stored it in unsigned int. Values above UINT_MAX could wrap before boundary calculation, causing subsequent TCP payload bytes to be treated as another SIP message and passed to the SDP parser. The stable fix preserves the wider type and rejects lengths exceeding the remaining payload.

Likely exposure

Likely exposure is limited to affected Linux kernels where the nf_conntrack_sip TCP helper is active and processes attacker-controlled SIP traffic. The bundle does not establish distribution defaults, appliance configurations, or vendor backport status. Consequently, kernel version strings alone may not reliably determine vulnerability.

Exploitation context

The CVSS vector describes network access, low complexity, no required privileges, and no user interaction. However, this CVE is not listed in KEV, and the supplied sources provide no evidence of active exploitation or a public proof of concept. Reachability of the vulnerable SIP-processing path remains essential.

Researcher notes

The demonstrated defect is an integer-width mismatch followed by incorrect SIP boundary handling. The fix changes clen to unsigned long and validates it against remaining TCP payload length. The bundle does not establish the precise downstream failure mode, affected distribution packages, a public exploit, or observed attacks; those points require vendor-specific confirmation.

Mitigation direction

  • Upgrade to a vendor-supported kernel release containing the applicable stable fix or documented backport.
  • Verify distribution and appliance advisories because packaged version numbers may not reveal backported fixes.
  • Prioritize reachable SIP gateways, firewalls, and other systems that process untrusted SIP-over-TCP traffic.
  • If patching is delayed, consult vendor guidance; the supplied sources name no supported interim workaround.

Validation and detection

  • Inventory kernel builds and determine whether the nf_conntrack_sip TCP helper is configured and active.
  • Confirm the installed source package contains the applicable stable fix or a vendor-documented equivalent backport.
  • Map network paths capable of delivering untrusted SIP-over-TCP traffic to the helper.
  • After updating, verify the running kernel changed and repeat the configuration and reachability checks.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2026-23457 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
1ADP providers
11Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.6CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H3.94.7Linux

Vulnerability scoring details

Base CVSS 3.1 score

8.6High
CVSS 3.1 vector shape for CVE-2026-23457Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxf5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35da, f5b321bd37fbec9188feb1f721ab46a5ac0b35daunaffected
LinuxLinux2.6.34, 0, 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10, 7.0affected
Weakness

CWE details

No CWE listed

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