# CVE-2026-31685

> Vulnerability · severity: **CRITICAL** (CVSS 9.4).

## 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)`.

## Key facts

- **CVE ID:** CVE-2026-31685
- **Published:** 2026-04-25
- **CVSS severity:** CRITICAL
- **CVSS base score:** 9.4
- **CWE codes:** NVD-CWE-noinfo

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31685

## Citation

> AI Analytics. CVE-2026-31685. Retrieved 2026-07-23 from https://api.ai-analytics.org/cve/CVE-2026-31685. Derived from NIST NVD. Licensed CC0.

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