# CVE-2026-23455: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931()

> A missing length check in the Linux kernel's H.323 conntrack module allows out-of-bounds reads, potentially causing crashes or information disclosure.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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-2026-23455, DEBIAN-CVE-2026-23455, GHSA-gm78-p64f-gx97, ROOT-OS-DEBIAN-11-CVE-2026-23455, ROOT-OS-DEBIAN-12-CVE-2026-23455, ROOT-OS-DEBIAN-13-CVE-2026-23455, ROOT-OS-UBUNTU-2204-CVE-2026-23455, ROOT-OS-UBUNTU-2404-CVE-2026-23455, UBUNTU-CVE-2026-23455

## What is CVE-2026-23455?

CVE-2026-23455 is a critical memory corruption 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_h323: check for zero length in DecodeQ931()

In DecodeQ931(), the UserUserIE code path reads a 16-bit length from
the packet, then decrements it by 1 to skip the protocol discriminator
byte before passing it to DecodeH323_UserInformation(). If the encoded
length is 0, the decrement wraps to -1, which is then passed as a
large value to the decoder, leading to an out-of-bounds read.

Add a check to ensure len is positive after the decrement.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-23455?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23455?

Apply the vendor's patch.

## Is CVE-2026-23455 being exploited?

There is no known exploitation of CVE-2026-23455 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-2026-23455 and fix it if it is affected.

What it is: CVE-2026-23455 is a critical memory corruption 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-2026-23455 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-2026-23455/ (Markdown: https://insights.sbomify.com/CVE-2026-23455/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23455
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23455
- OSV: https://osv.dev/vulnerability/CVE-2026-23455

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23455/
Summaries are generated and may contain mistakes; the official description above is the record.