# CVE-2026-31495: netfilter: ctnetlink: use netlink policy range checks

> Improper validation of TCP window scale values in ctnetlink allows undefined behavior via shift operations, potentially causing kernel crashes.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Apr 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-83303, BELL-CVE-2026-31495, DEBIAN-CVE-2026-31495, GHSA-q87j-mxf4-249g, ROOT-OS-DEBIAN-11-CVE-2026-31495, ROOT-OS-DEBIAN-12-CVE-2026-31495, ROOT-OS-DEBIAN-13-CVE-2026-31495, ROOT-OS-UBUNTU-2204-CVE-2026-31495, ROOT-OS-UBUNTU-2404-CVE-2026-31495, UBUNTU-CVE-2026-31495

## What is CVE-2026-31495?

CVE-2026-31495 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ctnetlink: use netlink policy range checks

Replace manual range and mask validations with netlink policy
annotations in ctnetlink code paths, so that the netlink core rejects
invalid values early and can generate extack errors.

- CTA_PROTOINFO_TCP_STATE: reject values > TCP_CONNTRACK_SYN_SENT2 at
  policy level, removing the manual >= TCP_CONNTRACK_MAX check.
- CTA_PROTOINFO_TCP_WSCALE_ORIGINAL/REPLY: reject values > TCP_MAX_WSCALE
  (14). The normal TCP option parsing path already clamps to this value,
  but the ctnetlink path accepted 0-255, causing undefined behavior when
  used as a u32 shift count.
- CTA_FILTER_ORIG_FLAGS/REPLY_FLAGS: use NLA_POLICY_MASK with
  CTA_FILTER_F_ALL, removing the manual mask checks.
- CTA_EXPECT_FLAGS: use NLA_POLICY_MASK with NF_CT_EXPECT_MASK, adding
  a new mask define grouping all valid expect flags.

Extracted from a broader nf-next patch by Florian Westphal, scoped to
ctnetlink for the fixes tree.

## Which versions are affected by CVE-2026-31495?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31495?

Apply the vendor's patch.

## Is CVE-2026-31495 being exploited?

There is no known exploitation of CVE-2026-31495 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-2026-31495 and fix it if it is affected.

What it is: CVE-2026-31495 is a medium-severity vulnerability in Linux kernel, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31495 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-2026-31495/ (Markdown: https://insights.sbomify.com/CVE-2026-31495/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31495
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31495
- OSV: https://osv.dev/vulnerability/CVE-2026-31495

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31495/
Summaries are generated and may contain mistakes; the official description above is the record.