---
id: CVE-2025-40173
title: 'net/ip6_tunnel: Prevent perpetual tunnel growth'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/ip6_tunnel: Prevent perpetual tunnel growth

  Similarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too.
  While ipv4 tunnel headroom adjustment growth …
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    566f8d5c8a443f2dd69c5460fdec43ed1c870c65
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    11f6066af3bfb8149aa16c42c0b0c5ea5b199a94
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    402b6985e872b4cf394bbbf33b503947a326a6cb
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    10fe967efe73c610e526ff7460581610633dee9c
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    48294a67863c9cfa367abb66bbf0ef6548ae124f
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    eeb4345488672584db4f8c20a1ae13a212ce31c4
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    b6eb25d870f1a8ae571fd3da2244b71df547824b
  - >-
    Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 <
    21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16
  - Linux 4.7
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-15T21:57:37.658529Z'
published: '2025-11-12'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:02:39.584Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-40173'
references:
  - url: 'https://git.kernel.org/stable/c/566f8d5c8a443f2dd69c5460fdec43ed1c870c65'
  - url: 'https://git.kernel.org/stable/c/11f6066af3bfb8149aa16c42c0b0c5ea5b199a94'
  - url: 'https://git.kernel.org/stable/c/402b6985e872b4cf394bbbf33b503947a326a6cb'
  - url: 'https://git.kernel.org/stable/c/10fe967efe73c610e526ff7460581610633dee9c'
  - url: 'https://git.kernel.org/stable/c/48294a67863c9cfa367abb66bbf0ef6548ae124f'
  - url: 'https://git.kernel.org/stable/c/eeb4345488672584db4f8c20a1ae13a212ce31c4'
  - url: 'https://git.kernel.org/stable/c/b6eb25d870f1a8ae571fd3da2244b71df547824b'
  - url: 'https://git.kernel.org/stable/c/21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16'
tags:
  - cve.org
epss: 0.00153
epssPercentile: 0.03999
ingestedAt: '2026-10-15T22:48:25.549Z'
---

## Overview

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

net/ip6_tunnel: Prevent perpetual tunnel growth

Similarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too.
While ipv4 tunnel headroom adjustment growth was limited in
commit 5ae1e9922bbd ("net: ip_tunnel: prevent perpetual headroom growth"),
ipv6 tunnel yet increases the headroom without any ceiling.

Reflect ipv4 tunnel headroom adjustment limit on ipv6 version.

Credits to Francesco Ruggeri, who was originally debugging this issue
and wrote local Arista-specific patch and a reproducer.

## Affected

- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 566f8d5c8a443f2dd69c5460fdec43ed1c870c65`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 11f6066af3bfb8149aa16c42c0b0c5ea5b199a94`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 402b6985e872b4cf394bbbf33b503947a326a6cb`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 10fe967efe73c610e526ff7460581610633dee9c`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 48294a67863c9cfa367abb66bbf0ef6548ae124f`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < eeb4345488672584db4f8c20a1ae13a212ce31c4`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < b6eb25d870f1a8ae571fd3da2244b71df547824b`
- `Linux >= 8eb30be0352d09165e94a41fef1c7b994dca0714 < 21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16`
- `Linux 4.7`

## Remediation

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