CVE-2026-31657 batman-adv: hold claim backbone gateways by reference
A use-after-free vulnerability in the batman-adv kernel module allows attackers to cause a denial of service or potentially execute code via improper reference handling.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31657?
CVE-2026-31657 is a critical use after free vulnerability in Linux kernel, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
batman-adv: hold claim backbone gateways by reference
batadv_bla_add_claim() can replace claim->backbone_gw and drop the old gateway's last reference while readers still follow the pointer.
The netlink claim dump path dereferences claim->backbone_gw->orig and takes claim->backbone_gw->crc_lock without pinning the underlying backbone gateway. batadv_bla_check_claim() still has the same naked pointer access pattern.
Reuse batadv_bla_claim_get_backbone_gw() in both readers so they operate on a stable gateway reference until the read-side work is complete. This keeps the dump and claim-check paths aligned with the lifetime rules introduced for the other BLA claim readers.
Which versions are affected by CVE-2026-31657?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31657?
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-2026-31657 being exploited?
There is no known exploitation of CVE-2026-31657 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-83810, BELL-CVE-2026-31657, DEBIAN-CVE-2026-31657, GHSA-w24x-3wrx-8q34, ROOT-OS-DEBIAN-11-CVE-2026-31657, ROOT-OS-DEBIAN-12-CVE-2026-31657 and 3 more.