# CVE-2026-68137: net/x25: fix use-after-free in x25_kill_by_neigh()

> A use-after-free in the Linux kernel X.25 network stack allows attackers to execute arbitrary code or escalate privileges via concurrent socket operations.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** BELL-CVE-2026-68137, DEBIAN-CVE-2026-68137, GHSA-8pjr-r8qw-rq6v, UBUNTU-CVE-2026-68137

## What is CVE-2026-68137?

CVE-2026-68137 is a critical use after free vulnerability in Linux, published on 10 Aug 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:

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().

## Which versions are affected by CVE-2026-68137?


## How do I fix CVE-2026-68137?

Apply the vendor's patch.

## Is CVE-2026-68137 being exploited?

There is no known exploitation of CVE-2026-68137 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68137 and fix it if it is affected.

What it is: CVE-2026-68137 is a critical use after free vulnerability in Linux, published on 10 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-68137 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-68137/ (Markdown: https://insights.sbomify.com/CVE-2026-68137/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68137
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68137
- OSV: https://osv.dev/vulnerability/CVE-2026-68137

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68137/
Summaries are generated and may contain mistakes; the official description above is the record.