CVE-2026-89951 batman-adv: fix stale receive device on merged fragments
A use-after-free vulnerability in the Linux kernel's batman-adv module allows attackers to cause a denial of service via stale device references in merged fragments.
- 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-2026-89951?
CVE-2026-89951 is a high-severity use after free vulnerability in Linux, published on 16 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:
batman-adv: fix stale receive device on merged fragments
Fragment reassembly reuses the skb from the highest-numbered buffered fragment as the merged packet. When that fragment was received on a hard interface which is deleted before the chain completes, the merged skb can re-enter the receive path with a stale skb->dev and skb_iif.
batadv_batman_skb_recv() passes such merged packets through the normal receive handlers again. DAT and bridge loop avoidance both derive the ARP header length from skb->dev, so they can dereference the freed net_device before the packet reaches the local mesh interface.
Refresh the receive device metadata from the current receive device before running the packet handlers. This keeps internally reinjected merged fragments consistent with the normal receive path after hard interface teardown.
Which versions are affected by CVE-2026-89951?
How do I fix CVE-2026-89951?
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-2026-89951 being exploited?
There is no known exploitation of CVE-2026-89951 in the wild and no public exploit code.
Sources
Also known as AZL-101675, BELL-CVE-2026-89951, DEBIAN-CVE-2026-89951, GHSA-27vc-6rpf-73gh, UBUNTU-CVE-2026-89951.