---
id: CVE-2026-80793
title: 'ipv4: reject undersized MTUs in ip_do_fragment()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv4: reject undersized MTUs in ip_do_fragment()

  ip_do_fragment() subtracts the IPv4 header length from the effective
  MTU and passes the resulting payload MTU to ip_fr…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    a716a64a4ba68cd46f2745fba2b1099fe8e0aa59
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    515b6816ba0c12d8415c88e5f41e6ec029e35cfa
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    74ce7389f8f562d39015f59a00ef7ad6acd37803
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    b0ea911453ce7210e8200a07a94d2458bd1e6430
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    36e0741833bd823866f8cb9f112f37cea1a70b60
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    d9d1a676b033acabf8e5645f730486d1f8204a3f
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    3556beb8ca86677af2aca5bfbed6f8e790fccc83
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    c8a74adccaf028223054633b532593101dfcc581
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    c0726f0caf8c6b3208552949e17d23634a2f3129
  - Linux 2.6.12
published: '2026-09-04'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:43:46.499Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-80793'
references:
  - url: 'https://git.kernel.org/stable/c/a716a64a4ba68cd46f2745fba2b1099fe8e0aa59'
  - url: 'https://git.kernel.org/stable/c/515b6816ba0c12d8415c88e5f41e6ec029e35cfa'
  - url: 'https://git.kernel.org/stable/c/74ce7389f8f562d39015f59a00ef7ad6acd37803'
  - url: 'https://git.kernel.org/stable/c/b0ea911453ce7210e8200a07a94d2458bd1e6430'
  - url: 'https://git.kernel.org/stable/c/36e0741833bd823866f8cb9f112f37cea1a70b60'
  - url: 'https://git.kernel.org/stable/c/d9d1a676b033acabf8e5645f730486d1f8204a3f'
  - url: 'https://git.kernel.org/stable/c/3556beb8ca86677af2aca5bfbed6f8e790fccc83'
  - url: 'https://git.kernel.org/stable/c/c8a74adccaf028223054633b532593101dfcc581'
  - url: 'https://git.kernel.org/stable/c/c0726f0caf8c6b3208552949e17d23634a2f3129'
tags:
  - cve.org
epss: 0.00195
epssPercentile: 0.08586
ingestedAt: '2026-10-19T09:16:01.530Z'
---

## Overview

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

ipv4: reject undersized MTUs in ip_do_fragment()

ip_do_fragment() subtracts the IPv4 header length from the effective
MTU and passes the resulting payload MTU to ip_frag_next().

If the effective MTU is smaller than hlen + 8, ip_frag_next() rounds
the fragment payload length down to zero. The fragmentation state then
never makes forward progress: state->left, state->ptr and state->offset
stay unchanged while ip_do_fragment() keeps allocating and transmitting
header-only fragments until the softlockup detector fires.

This is reproducible with a route installed using "mtu lock 20", but it
is also reproducible without route MTU lock, for example by forwarding a
packet to a device whose MTU is 20.

Fix it in ip_do_fragment() by rejecting mtu < hlen + 8 with -EMSGSIZE,
matching the existing IPv6 fragmentation check.

## Affected

- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < a716a64a4ba68cd46f2745fba2b1099fe8e0aa59`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 515b6816ba0c12d8415c88e5f41e6ec029e35cfa`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 74ce7389f8f562d39015f59a00ef7ad6acd37803`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < b0ea911453ce7210e8200a07a94d2458bd1e6430`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 36e0741833bd823866f8cb9f112f37cea1a70b60`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < d9d1a676b033acabf8e5645f730486d1f8204a3f`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 3556beb8ca86677af2aca5bfbed6f8e790fccc83`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c8a74adccaf028223054633b532593101dfcc581`
- `Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c0726f0caf8c6b3208552949e17d23634a2f3129`
- `Linux 2.6.12`

## Remediation

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