---
id: CVE-2026-72502
title: 'tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)

  When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).
  This is interpreted by T…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    560b33b434e922ef97f9ff23aa2e909ef7aacd5c
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    21f69ac1879bb970588d5e7c12a96e6542f7c1a7
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    c0db3dc2ac323b6c4b76adede3b355a9daa6dea8
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    572fff10819dfc359298d1f774839e76a4d96f93
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    8e6214a530c03e341dc1b0a846c8f2b716b3551a
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    a210791f33345aa87187f7d7a9f3b9b7f4a28e6d
  - >-
    Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba <
    2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22
  - Linux 4.8
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-16T18:51:17.494885Z'
published: '2026-08-15'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T18:55:27.761Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-72502'
references:
  - url: 'https://git.kernel.org/stable/c/560b33b434e922ef97f9ff23aa2e909ef7aacd5c'
  - url: 'https://git.kernel.org/stable/c/21f69ac1879bb970588d5e7c12a96e6542f7c1a7'
  - url: 'https://git.kernel.org/stable/c/c0db3dc2ac323b6c4b76adede3b355a9daa6dea8'
  - url: 'https://git.kernel.org/stable/c/572fff10819dfc359298d1f774839e76a4d96f93'
  - url: 'https://git.kernel.org/stable/c/8e6214a530c03e341dc1b0a846c8f2b716b3551a'
  - url: 'https://git.kernel.org/stable/c/d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e'
  - url: 'https://git.kernel.org/stable/c/a210791f33345aa87187f7d7a9f3b9b7f4a28e6d'
  - url: 'https://git.kernel.org/stable/c/2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22'
tags:
  - cve.org
epss: 0.00716
epssPercentile: 0.52841
ingestedAt: '2026-10-16T19:46:24.389Z'
---

## Overview

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

tcp: ipv6: clamp default adverting MSS to avoid GSO_BY_FRAGS (0xFFFF)

When MTU is large, ip6_default_advmss() can return IPV6_MAXPLEN (65535).
This is interpreted by TCP as mss_clamp, allowing the MSS to reach 65535.

However, 0xFFFF is also used as a magic value GSO_BY_FRAGS in the kernel.
If a TCP packet with gso_size=0xFFFF is passed to skb_segment(), it will
be mistakenly treated as GSO_BY_FRAGS, leading to a NULL pointer
dereference because local TCP packets do not use frag_list.

Fix this by returning min(IPV6_MAXPLEN, GSO_BY_FRAGS - 1) (65534) from
ip6_default_advmss() when MTU is large.

Also update the stale comment in ip6_default_advmss() which suggested
that IPV6_MAXPLEN is returned to mean "any MSS".

## Affected

- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < 560b33b434e922ef97f9ff23aa2e909ef7aacd5c`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < 21f69ac1879bb970588d5e7c12a96e6542f7c1a7`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < c0db3dc2ac323b6c4b76adede3b355a9daa6dea8`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < 572fff10819dfc359298d1f774839e76a4d96f93`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < 8e6214a530c03e341dc1b0a846c8f2b716b3551a`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < d774cdbda6634a78d0f2baf201ee5a8c57f3bc0e`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < a210791f33345aa87187f7d7a9f3b9b7f4a28e6d`
- `Linux >= 3953c46c3ac7eef31a9935427371c6f54a22f1ba < 2bf43d0e2e6a27d52a7d624e2d6b9116972e8a22`
- `Linux 4.8`

## Remediation

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