---
id: CVE-2026-74657
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops

  fib_nlmsg_size() still estimates nexthop space as if every gateway is
  encoded as an IPv4 RTA_GATEWAY attribute
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops

  fib_nlmsg_size() still estimates nexthop space as if every gateway is
  encoded as an IPv4 RTA_GATEWAY attribute. IPv4 ro…
severity: none
published: '2026-08-22'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T13:10:00.187'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-74657'
references:
  - url: 'https://git.kernel.org/stable/c/0f0ca602941d0a81ae9514943ca06c55159c6385'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4a5dfbae5179f6574695012a980476254df2d295'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4ff9548d84945d2cbf9e4c207288063a200ea397'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/5307a53599fa762c06e475ee4a375252074fd324'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/57195f0ab5cfbb5ee0864e5aff15ceb48f5a5e28'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7f80ad373ce4a7af5367ff273cea0f16e91387f3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9b22f13524fa0de0d963bbd3002df6c28bae3395'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a59edda6eda1252340354322d8ab318b2e9052fb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00177
epssPercentile: 0.06714
ingestedAt: '2026-10-14T13:30:58.529Z'
---

## Overview

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

ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops

fib_nlmsg_size() still estimates nexthop space as if every gateway is
encoded as an IPv4 RTA_GATEWAY attribute. IPv4 routes can also carry an
IPv6 gateway, which fib_nexthop_info() dumps as RTA_VIA.

As a result, route notifications can allocate an skb that is too small.
fib_dump_info() then fails with -EMSGSIZE and rtmsg_fib() hits the
WARN_ON() that marks such failures as a fib_nlmsg_size() bug. With
panic_on_warn set, this becomes a kernel panic.

Mirror the actual nexthop dump layout in fib_nlmsg_size(): account for
IPv6 nexthop gateways dumped as RTA_VIA, for the no-header rtnexthop
layout used inside RTA_MULTIPATH, and for RTA_FLOW only when it is
actually present.

## Remediation

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