---
id: CVE-2026-63992
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

  In some cases, iptunnel_pmtud_check_icmp() can be called while
  skb transport header is not set.
  …
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

  In some cases, iptunnel_pmtud_check_icmp() can be called while
  skb transport header is not set.
  …
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'
cwe:
  - CWE-125
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.9, < 5.10.259'
  - 'linux_kernel >= 5.11, < 5.15.210'
  - 'linux_kernel >= 5.16, < 6.1.176'
  - 'linux_kernel >= 6.2, < 6.6.143'
  - 'linux_kernel >= 6.7, < 6.12.93'
  - 'linux_kernel >= 6.13, < 6.18.35'
  - 'linux_kernel >= 6.19, < 7.0.12'
  - linux_kernel = 7.1
patched:
  - linux_kernel 7.0.12
published: '2026-07-19'
updated: '2026-10-07'
sourceUpdated: '2026-10-07T20:29:43.487'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63992'
references:
  - url: 'https://git.kernel.org/stable/c/43368636c663cff6e59dde93cf4b8e43ac28eb93'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/509323077ef79a26ba0c60bb556e45c12c398b2d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/5a92cb45e34749865d03daf8d3500f77b5f6644c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7f4f7efe7f30edd29c4988de01728bf2398217e4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a096b6e34f602950af9a2b0856cd93a5f4c276d7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c7b7ec3e69e673c0d6b57f74d21da50c485c598e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cb549df9ce4ee15c9d5b19ddab12cf2128e4313c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00514
epssPercentile: 0.41838
ingestedAt: '2026-10-07T20:46:46.957Z'
---

## Overview

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

tunnels: do not assume transport header in iptunnel_pmtud_check_icmp()

In some cases, iptunnel_pmtud_check_icmp() can be called while
skb transport header is not set.

This triggers an out-of-bound access, because
(typeof(skb->transport_header))~0U is 65535.

Access the icmp header based on IPv4 network header,
after making sure icmp->type is present in skb linear part.

Note that iptunnel_pmtud_check_icmpv6()) is fine.

## Affected

- `linux_kernel >= 5.9, < 5.10.259`
- `linux_kernel >= 5.11, < 5.15.210`
- `linux_kernel >= 5.16, < 6.1.176`
- `linux_kernel >= 6.2, < 6.6.143`
- `linux_kernel >= 6.7, < 6.12.93`
- `linux_kernel >= 6.13, < 6.18.35`
- `linux_kernel >= 6.19, < 7.0.12`
- `linux_kernel = 7.1`

## Remediation

Upgrade past the affected range:

- `linux_kernel 7.0.12`