---
id: CVE-2026-99041
title: 'ip6_gre: remove obsolete ERSPAN PMTU update'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ip6_gre: remove obsolete ERSPAN PMTU update

  A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb,
  and mirred can redirect it to a native ip6erspan devi…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 <
    b14a682ad7d45345701e08f9279d483a1da8b36c
  - >-
    Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 <
    f5b143f4cd3fb7673df8d727550478a4b762908a
  - >-
    Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 <
    2d06cb25a497d3a7034ef9d172626c2d6620a0f1
  - >-
    Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 <
    8f27260b989f488760289276377db24fbfb20bfa
  - >-
    Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 <
    8bc60db48e8cba35488bbd6e1f94aa990afa275a
  - Linux 4.16
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:22:00.403Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99041'
references:
  - url: 'https://git.kernel.org/stable/c/b14a682ad7d45345701e08f9279d483a1da8b36c'
  - url: 'https://git.kernel.org/stable/c/f5b143f4cd3fb7673df8d727550478a4b762908a'
  - url: 'https://git.kernel.org/stable/c/2d06cb25a497d3a7034ef9d172626c2d6620a0f1'
  - url: 'https://git.kernel.org/stable/c/8f27260b989f488760289276377db24fbfb20bfa'
  - url: 'https://git.kernel.org/stable/c/8bc60db48e8cba35488bbd6e1f94aa990afa275a'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.526Z'
---

## Overview

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

ip6_gre: remove obsolete ERSPAN PMTU update

A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb,
and mirred can redirect it to a native ip6erspan device. The legacy PMTU
update in ip6erspan_tunnel_xmit() treats that metadata dst as a route.
Since it has no output device, dst_dev(dst)->mtu dereferences NULL.

On v7.2 with KASAN, an initial UID/GID 65534 process with CapEff 0 used
self-created user and network namespaces to trigger:

  KASAN: null-ptr-deref
  RIP: ip6erspan_tunnel_xmit+0x10fc/0x2cc0
  Kernel panic - not syncing: Fatal exception in interrupt

The update is obsolete. Commit fe1a4ca0a2b7 ("ip6_gre: process toobig
in a better way") changed IPv6 GRE Too Big handling to update the
underlay route and removed the equivalent block from __gre6_xmit().
ip6_tnl_xmit() then propagates the underlay PMTU to the overlay route.

Remove the stale ERSPAN copy and its now-unused dst variable. This
eliminates the metadata-dst dereference and keeps ERSPAN aligned with
IPv6 GRE PMTU handling.

## Affected

- `Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 < b14a682ad7d45345701e08f9279d483a1da8b36c`
- `Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 < f5b143f4cd3fb7673df8d727550478a4b762908a`
- `Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 < 2d06cb25a497d3a7034ef9d172626c2d6620a0f1`
- `Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 < 8f27260b989f488760289276377db24fbfb20bfa`
- `Linux >= 5a963eb61b7c39e6c422b6e48619d19d04719358 < 8bc60db48e8cba35488bbd6e1f94aa990afa275a`
- `Linux 4.16`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.