# CVE-2026-80733: net: remove WARN_ON_ONCE() from sk_mc_loop()

> A local attacker can trigger a kernel warning via raw sockets, potentially causing a denial of service in the Linux kernel.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** AZL-99048, BELL-CVE-2026-80733, DEBIAN-CVE-2026-80733, GHSA-mf9r-r7x5-32qq, UBUNTU-CVE-2026-80733

## What is CVE-2026-80733?

CVE-2026-80733 is a denial of service vulnerability in Linux, published on 3 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

net: remove WARN_ON_ONCE() from sk_mc_loop()

sk_mc_loop() can be called for sockets that are neither AF_INET
nor AF_INET6 (e.g. AF_PACKET sockets when sending packets via raw/packet
socket over virtual devices such as VRF or ipvlan).

In such cases, sk_family is not AF_INET/AF_INET6 and sk_mc_loop() falls
through the switch statement and triggers WARN_ON_ONCE(1).

Non-INET sockets do not support IP_MULTICAST_LOOP or IPV6_MULTICAST_LOOP
options, so loopback should default to true without generating a warning.

## Which versions are affected by CVE-2026-80733?


## How do I fix CVE-2026-80733?

Apply the vendor's patch.

## Is CVE-2026-80733 being exploited?

There is no known exploitation of CVE-2026-80733 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80733 and fix it if it is affected.

What it is: CVE-2026-80733 is a denial of service vulnerability in Linux, published on 3 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80733 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-2026-80733/ (Markdown: https://insights.sbomify.com/CVE-2026-80733/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80733
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80733
- OSV: https://osv.dev/vulnerability/CVE-2026-80733

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80733/
Summaries are generated and may contain mistakes; the official description above is the record.