CVE-2026-98026 net: bridge: mcast: properly convert mglist to rcu
A use-after-free vulnerability in the Linux kernel bridge multicast code allows local attackers to cause a denial of service or potentially execute code.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98026?
CVE-2026-98026 is an use after free vulnerability in Linux, published on 25 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: bridge: mcast: properly convert mglist to rcu
Sashiko reported a bug [1] that br_multicast_del_port_group unlists the port group not using proper rcu helper that preserves the next pointer and after that immediately frees the port group without waiting for rcu grace period. The only rcu walker of mglist is br_multicast_list_adjacent() and it turns out that function has always been buggy because mglist was never properly converted to RCU. Fix it by converting it to rcu and moving its initialization after eth_addr's. Initializing p->next can use RCU_INIT_POINTER because we have a barrier from the hlist_add_head_rcu call later, besides we're initializing an unpublished structure anyway.
[1] https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260826014200.362304-1-littleddfu%40gmail.com
Which versions are affected by CVE-2026-98026?
How do I fix CVE-2026-98026?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98026 being exploited?
There is no known exploitation of CVE-2026-98026 in the wild and no public exploit code.
Sources
Also known as AZL-104513, BELL-CVE-2026-98026, DEBIAN-CVE-2026-98026, GHSA-r366-wr25-m9fj, UBUNTU-CVE-2026-98026.