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

> An integer truncation in the Linux kernel SIP conntrack parser allows attackers to cause denial of service or unexpected parsing behavior via crafted SIP messages.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-23457, DEBIAN-CVE-2026-23457, GHSA-4q45-qq5w-x2fj, ROOT-OS-DEBIAN-11-CVE-2026-23457, ROOT-OS-DEBIAN-12-CVE-2026-23457, ROOT-OS-DEBIAN-13-CVE-2026-23457, ROOT-OS-UBUNTU-2204-CVE-2026-23457, ROOT-OS-UBUNTU-2404-CVE-2026-23457, UBUNTU-CVE-2026-23457

## What is CVE-2026-23457?

CVE-2026-23457 is a high-severity vulnerability in Linux kernel, published on 3 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-23457?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23457?

Apply the vendor's patch.

## Is CVE-2026-23457 being exploited?

There is no known exploitation of CVE-2026-23457 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23457 and fix it if it is affected.

What it is: CVE-2026-23457 is a high-severity vulnerability in Linux kernel, published on 3 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-23457 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23457/ (Markdown: https://insights.sbomify.com/CVE-2026-23457/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23457
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23457
- OSV: https://osv.dev/vulnerability/CVE-2026-23457

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23457/
Summaries are generated and may contain mistakes; the official description above is the record.