CVE-2026-89950 batman-adv: mcast: linearize skbuff for packet generation
A missing linearization check in the batman-adv multicast forwarding code can trigger a fatal kernel bug, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89950?
CVE-2026-89950 is a vulnerability in Linux, published on 16 Sep 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: mcast: linearize skbuff for packet generation
batadv_mcast_forw_packet() and batadv_mcast_forw_scrape() is not only called (indirectly) by the unsharing+linearizing batadv_recv_mcast_packet() handler. When it is called (indirectly) by batadv_mcast_forw_mcsend() then it will be unshared but not linearized. The SKB_LINEAR_ASSERT() can therefore cause a fatal BUG().
The linearization should happen during the expansion of the head because the scrape function can be hit already during the initial batadv_mcast_forw_mode() selection code:
* batadv_interface_tx * batadv_mcast_forw_mode * batadv_mcast_forw_mode_by_count() * batadv_mcast_forw_push() -> calls batadv_mcast_forw_expand_head() before everything else * batadv_mcast_forw_push_tvlvs() * batadv_mcast_forw_push_dests() * batadv_mcast_forw_push_adjust_padding() * batadv_mcast_forw_scrape()
Which versions are affected by CVE-2026-89950?
How do I fix CVE-2026-89950?
Apply the vendor's patch.
Is CVE-2026-89950 being exploited?
There is no known exploitation of CVE-2026-89950 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89950, DEBIAN-CVE-2026-89950, GHSA-3h9h-h4qr-r799, UBUNTU-CVE-2026-89950.