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.
- 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
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-80733 being exploited?
There is no known exploitation of CVE-2026-80733 in the wild and no public exploit code.
Sources
Also known as AZL-99048, BELL-CVE-2026-80733, DEBIAN-CVE-2026-80733, GHSA-mf9r-r7x5-32qq, UBUNTU-CVE-2026-80733.