# CVE-2026-31685: netfilter: ip6t_eui64: reject invalid MAC header for all packets

> A missing check in the Linux kernel's ip6t_eui64 module allows accessing an invalid MAC header, potentially causing a null pointer dereference and system crash.

- **Severity:** Critical 9.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 25 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-84201, BELL-CVE-2026-31685, DEBIAN-CVE-2026-31685, GHSA-hf2p-g3jq-w2mx, ROOT-OS-DEBIAN-11-CVE-2026-31685, ROOT-OS-DEBIAN-12-CVE-2026-31685, ROOT-OS-UBUNTU-2204-CVE-2026-31685, ROOT-OS-UBUNTU-2404-CVE-2026-31685, UBUNTU-CVE-2026-31685

## What is CVE-2026-31685?

CVE-2026-31685 is a critical vulnerability in Linux kernel, published on 25 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: ip6t_eui64: reject invalid MAC header for all packets

`eui64_mt6()` derives a modified EUI-64 from the Ethernet source address
and compares it with the low 64 bits of the IPv6 source address.

The existing guard only rejects an invalid MAC header when
`par->fragoff != 0`. For packets with `par->fragoff == 0`, `eui64_mt6()`
can still reach `eth_hdr(skb)` even when the MAC header is not valid.

Fix this by removing the `par->fragoff != 0` condition so that packets
with an invalid MAC header are rejected before accessing `eth_hdr(skb)`.

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

## Which versions are affected by CVE-2026-31685?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31685?

Apply the vendor's patch.

## Is CVE-2026-31685 being exploited?

There is no known exploitation of CVE-2026-31685 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-2026-31685 and fix it if it is affected.

What it is: CVE-2026-31685 is a critical vulnerability in Linux kernel, published on 25 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-2026-31685 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-2026-31685/ (Markdown: https://insights.sbomify.com/CVE-2026-31685/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31685
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31685
- OSV: https://osv.dev/vulnerability/CVE-2026-31685

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31685/
Summaries are generated and may contain mistakes; the official description above is the record.