# CVE-2026-52999: netfilter: nfnetlink_osf: fix out-of-bounds read on option matching

> An out-of-bounds read in the Linux kernel netfilter OSF module allows attackers to read garbage data when logging is enabled.

- **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:** 24 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-52999, DEBIAN-CVE-2026-52999, GHSA-vhgw-q6q5-v9w3, ROOT-OS-DEBIAN-11-CVE-2026-52999, ROOT-OS-DEBIAN-12-CVE-2026-52999, ROOT-OS-UBUNTU-2204-CVE-2026-52999, ROOT-OS-UBUNTU-2404-CVE-2026-52999, UBUNTU-CVE-2026-52999

## What is CVE-2026-52999?

CVE-2026-52999 is a critical vulnerability in Linux kernel, published on 24 Jun 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: nfnetlink_osf: fix out-of-bounds read on option matching

In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once
and passed by reference to nf_osf_match_one() for each fingerprint
checked. During TCP option parsing, nf_osf_match_one() advances the
shared ctx->optp pointer.

If a fingerprint perfectly matches, the function returns early without
restoring ctx->optp to its initial state. If the user has configured
NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint.
However, because ctx->optp was not restored, the next call to
nf_osf_match_one() starts parsing from the end of the options buffer.
This causes subsequent matches to read garbage data and fail
immediately, making it impossible to log more than one match or logging
incorrect matches.

Instead of using a shared ctx->optp pointer, pass the context as a
constant pointer and use a local pointer (optp) for TCP option
traversal. This makes nf_osf_match_one() strictly stateless from the
caller's perspective, ensuring every fingerprint check starts at the
correct option offset.

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

## Which versions are affected by CVE-2026-52999?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52999?

Apply the vendor's patch.

## Is CVE-2026-52999 being exploited?

There is no known exploitation of CVE-2026-52999 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-2026-52999 and fix it if it is affected.

What it is: CVE-2026-52999 is a critical vulnerability in Linux kernel, published on 24 Jun 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-2026-52999 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-2026-52999/ (Markdown: https://insights.sbomify.com/CVE-2026-52999/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52999
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52999
- OSV: https://osv.dev/vulnerability/CVE-2026-52999

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52999/
Summaries are generated and may contain mistakes; the official description above is the record.