CVE-2026-63834 batman-adv: tp_meter: restrict number of unacked list entries
An attacker can cause a denial of service in the Linux kernel's batman-adv module by exhausting memory or CPU resources via crafted network packets.
- 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-2026-63834?
CVE-2026-63834 is a denial of service vulnerability in Linux, published on 19 Jul 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: tp_meter: restrict number of unacked list entries
When the unacked_list is unbound, an attacker could send messages with small lengths and appropriated seqno + gaps to force the receiver to allocate more and more unacked_list entries. And the end either causing an out-of-memory situation or increase the management overhead for the (large) list that significant portions of CPU cycles are wasted in searching through the list.
When limiting the list to a specific number, it is important to still correctly add a new entry to the list. But if the list became larger than the limit, the last entry of the list (with the highest seqno) must be dropped to still allow the earlier seqnos to finish and therefore to continue the process. Otherwise, the process might get stuck with too high seqnos which are not handled by batadv_tp_ack_unordered().
Which versions are affected by CVE-2026-63834?
How do I fix CVE-2026-63834?
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-2026-63834 being exploited?
There is no known exploitation of CVE-2026-63834 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-63834, DEBIAN-CVE-2026-63834, GHSA-946h-284m-vvp5, ROOT-OS-DEBIAN-11-CVE-2026-63834, ROOT-OS-UBUNTU-2204-CVE-2026-63834, UBUNTU-CVE-2026-63834.