---
id: "CVE-2026-99072"
kind: "vulnerability"
aliases: ["CVE-2026-99072"]
title: "Linux kernel IPv4: route notification crashes when nexthop group shrinks"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "linux-kernel", "networking", "routers"]
not_affected_if: []
published_at: "2026-10-23T13:17:31+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T04:53:44+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99072", "first_seen_at": "2026-10-23T21:57:34+00:00"}]
---

# Linux kernel IPv4: route notification crashes when nexthop group shrinks

A race in the Linux kernel's IPv4 route notification code can dereference a NULL pointer when a nexthop group is replaced with fewer paths during the size calculation. The sources do not state what an attacker can gain beyond a kernel crash.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `uname -r` and compare against the fixed kernel versions in your distribution's advisory
- unknown whether the sources list specific affected kernel versions

## Fix

- Update the Linux kernel to a release that includes the upstream commit resolving this ipv4 fix
- unknown which exact kernel versions carry the fix, as the sources do not say

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99072

## From the sources

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

ipv4: stop route notification sizing when nexthop group shrinks

Commit 680aea08e78c ("net: ipv4: Emit notification when fib
hardware flags are changed") added an RCU-only fib_nlmsg_size() call
for asynchronous hardware flag notifications.

fib_nlmsg_size() checks fib_info_num_path() before each iteration,
then fib_info_nhc() independently reloads nh->nh_grp. If
RTM_NEWNEXTHOP replaces a group with fewer paths between those loads,
fib_info_nhc() returns NULL and fib_nexthop_nlmsg_size() dereferences
it.

Stop sizing when the indexed path is absent. Nexthop groups are
dense, so the current snapshot has no later path.

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