---
id: CVE-2026-63994
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  tunnels: load network headers after skb_cow() in
  iptunnel_pmtud_build_icmp[v6]()


  Sashiko found that iptunnel_pmtud_build_icmp() and

  iptunnel_pmtud_build_icmpv6() were …
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  tunnels: load network headers after skb_cow() in
  iptunnel_pmtud_build_icmp[v6]()


  Sashiko found that iptunnel_pmtud_build_icmp() and

  iptunnel_pmtud_build_icmpv6() were …
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
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: '2026-10-07T20:28:32.877'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63994'
references:
  - url: 'https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00514
epssPercentile: 0.4184
ingestedAt: '2026-10-07T20:46:46.957Z'
---

## Overview

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

tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()

Sashiko found that iptunnel_pmtud_build_icmp() and
iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr()
before an skb_cow() call which can reallocate skb->head.

Fix this possible UAF by initializing the local variables
after the skb_cow() call.

Remove skb_reset_network_header() calls which were not needed.

## 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`