CVE-2025-21781 batman-adv: fix panic during interface removal
A null pointer dereference in the batman-adv kernel module during interface removal can cause a system crash, requiring a kernel patch.
- 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-2025-21781?
CVE-2025-21781 is a medium-severity vulnerability in Linux kernel, published on 27 Feb 2025. 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 panic during interface removal
Reference counting is used to ensure that batadv_hardif_neigh_node and batadv_hard_iface are not freed before/during batadv_v_elp_throughput_metric_update work is finished.
But there isn't a guarantee that the hard if will remain associated with a soft interface up until the work is finished.
This fixes a crash triggered by reboot that looks like this:
Call trace: batadv_v_mesh_free+0xd0/0x4dc [batman_adv] batadv_v_elp_throughput_metric_update+0x1c/0xa4 process_one_work+0x178/0x398 worker_thread+0x2e8/0x4d0 kthread+0xd8/0xdc ret_from_fork+0x10/0x20
(the batadv_v_mesh_free call is misleading, and does not actually happen)
I was able to make the issue happen more reliably by changing hardif_neigh->bat_v.metric_work work to be delayed work. This allowed me to track down and confirm the fix.
[[email protected]: prevent entering batadv_v_elp_get_throughput without soft_iface]
Which versions are affected by CVE-2025-21781?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21781?
Apply the vendor's patch.
Is CVE-2025-21781 being exploited?
There is no known exploitation of CVE-2025-21781 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21781, DEBIAN-CVE-2025-21781, GHSA-5v2w-fx47-6rq2, ROOT-OS-UBUNTU-2404-CVE-2025-21781, UBUNTU-CVE-2025-21781.