---
id: CVE-2026-99074
title: 'ipv4: stop PMTU walk when nexthop group shrinks'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv4: stop PMTU walk when nexthop group shrinks

  Commit 7d3f3b4367f3 ("net: ipv4: Cache pmtu for all packet paths if
  multipath enabled") made __ip_rt_update_pmtu() upda…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 3bed2abab4a682d426624ce9add9d7b6d475d4e4 <
    7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a
  - >-
    Linux >= 7f5005457b3072fe1ddf15bfef869f2a1d98e05e <
    c60d17d6dd61adc761ac6f65a008fefbc54cbf87
  - >-
    Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 <
    c6d670ac656badfd0e15355e07a13a6bdf3b69fd
  - >-
    Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 <
    f27483f9975b5065ff67054cc7eb8edac6083488
  - >-
    Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 <
    6619e01855e65ef35723685a557e3eb106f4ecf5
  - Linux fc07a232326a623d0be482e307c08ea7049c2846
  - Linux b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e
  - Linux >= 6.6.79 < 6.6.160
  - Linux >= 6.12.16 < 6.12.113
  - Linux >= 5.15.179 < 5.16
  - Linux >= 6.1.129 < 6.2
  - Linux 6.13
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:23:17.866Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99074'
references:
  - url: 'https://git.kernel.org/stable/c/7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a'
  - url: 'https://git.kernel.org/stable/c/c60d17d6dd61adc761ac6f65a008fefbc54cbf87'
  - url: 'https://git.kernel.org/stable/c/c6d670ac656badfd0e15355e07a13a6bdf3b69fd'
  - url: 'https://git.kernel.org/stable/c/f27483f9975b5065ff67054cc7eb8edac6083488'
  - url: 'https://git.kernel.org/stable/c/6619e01855e65ef35723685a557e3eb106f4ecf5'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.513Z'
---

## Overview

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

ipv4: stop PMTU walk when nexthop group shrinks

Commit 7d3f3b4367f3 ("net: ipv4: Cache pmtu for all packet paths if
multipath enabled") made __ip_rt_update_pmtu() update every path.

For nexthop objects, fib_info_num_path() and fib_info_nhc()
independently load nh->nh_grp.  RCU protects each group's lifetime but
does not make the loads observe the same group.  If replacement shrinks
the group after the loop accepts an index, fib_info_nhc() returns NULL
and update_or_create_fnhe() dereferences it.

A deterministic probe only widened the existing window between the real
operations.  On v7.2, an RTM_NEWNEXTHOP replacement published a
one-member group after the PMTU reader accepted index 1 from a two-member
group, producing:

  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: update_or_create_fnhe+0x45/0x15b0

Stop when the indexed path is absent.  Groups are dense, so no later
index exists in that snapshot.  The same real-writer window completed
114,423 PMTU iterations without an oops with this check.  A reproducer
is available on request.

Replacement requires CAP_NET_ADMIN in the network namespace.  Where
unprivileged user namespaces are permitted, a local user can obtain it
in a new user and network namespace.

## Affected

- `Linux >= 3bed2abab4a682d426624ce9add9d7b6d475d4e4 < 7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a`
- `Linux >= 7f5005457b3072fe1ddf15bfef869f2a1d98e05e < c60d17d6dd61adc761ac6f65a008fefbc54cbf87`
- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < c6d670ac656badfd0e15355e07a13a6bdf3b69fd`
- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < f27483f9975b5065ff67054cc7eb8edac6083488`
- `Linux >= 7d3f3b4367f315a61fc615e3138f3d320da8c466 < 6619e01855e65ef35723685a557e3eb106f4ecf5`
- `Linux fc07a232326a623d0be482e307c08ea7049c2846`
- `Linux b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e`
- `Linux >= 6.6.79 < 6.6.160`
- `Linux >= 6.12.16 < 6.12.113`
- `Linux >= 5.15.179 < 5.16`
- `Linux >= 6.1.129 < 6.2`
- `Linux 6.13`

## Remediation

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