# CVE-2026-99072: ipv4: stop route notification sizing when nexthop group shrinks


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110966, BELL-CVE-2026-99072, DEBIAN-CVE-2026-99072, GHSA-wrfx-ch9c-5jj2, UBUNTU-CVE-2026-99072

## What is CVE-2026-99072?

CVE-2026-99072 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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.

## Which versions are affected by CVE-2026-99072?


## How do I fix CVE-2026-99072?

Upgrade to a fixed version.

## Is CVE-2026-99072 being exploited?

There is no known exploitation of CVE-2026-99072 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99072 and fix it if it is affected.

What it is: CVE-2026-99072 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99072 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-99072/ (Markdown: https://insights.sbomify.com/CVE-2026-99072/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99072
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99072
- OSV: https://osv.dev/vulnerability/CVE-2026-99072

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99072/
Summaries are generated and may contain mistakes; the official description above is the record.