CVE-2026-80839 batman-adv: reject unrepresentable multicast TVLV offsets
An attacker can trigger memory corruption in the Linux kernel batman-adv module by sending crafted multicast TVLV packets, potentially leading to code execution or system crash.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-80839?
CVE-2026-80839 is a memory corruption vulnerability in Linux, published on 4 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: reject unrepresentable multicast TVLV offsets
The network and transport header fields in struct sk_buff are 16-bit offsets from skb->head, and U16_MAX is reserved as the unset transport header value. batadv_tvlv_call_handler() sets both fields from a received multicast TVLV without checking whether the TVLV end is representable.
If the end offset exceeds the field's range, skb_set_transport_header() truncates it so that the transport header precedes the network header. The negative difference is then returned by skb_network_header_len() as a large u32. batadv_mcast_forw_packet() consequently accepts an oversized multicast tracker and accesses memory beyond the skb data.
Add skb_set_transport_header_careful(), an offset-aware counterpart to skb_reset_transport_header_careful(), which validates the final head-relative offset before assigning it. Use the new helper in batadv_tvlv_call_handler() and reject unrepresentable TVLVs before setting the network header.
Which versions are affected by CVE-2026-80839?
How do I fix CVE-2026-80839?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-80839 being exploited?
There is no known exploitation of CVE-2026-80839 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-80839, DEBIAN-CVE-2026-80839, GHSA-676r-cqgf-36vf, UBUNTU-CVE-2026-80839.