# CVE-2026-74628: net/x25: fix use-after-free of the socket by its timers

> A use-after-free vulnerability in the Linux kernel's X.25 networking subsystem allows attackers to cause denial of service or potentially execute code via timer race conditions.

- **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:** 22 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** AZL-97077, BELL-CVE-2026-74628, DEBIAN-CVE-2026-74628, GHSA-fp3m-qh7p-hcj7, UBUNTU-CVE-2026-74628

## What is CVE-2026-74628?

CVE-2026-74628 is a critical use after free vulnerability in Linux, published on 22 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 of the socket by its timers

The x25 timers are armed with mod_timer() and cancelled with
timer_delete(), so a pending timer holds no reference on the socket and a
cancel does not wait for a callback already running on another CPU.

x25_heartbeat_expiry() also rearms unconditionally, so it can reinstall
sk->sk_timer after __x25_destroy_socket() has passed its cancel point.
The following __sock_put() frees the socket while the timer is still
queued, and the next expiry uses freed memory.  KASAN reports a
slab-use-after-free on the kmalloc-2k object freed by close().

timer_delete_sync() cannot be used here: x25_heartbeat_expiry() and
x25_timer_expiry() both reach the cancels from inside the timer they
would wait on, through __x25_destroy_socket() and x25_disconnect().

Arm the timers with sk_reset_timer() and cancel them with sk_stop_timer()
so that an armed timer owns a reference, and release it in both expiry
handlers.  Rearm the heartbeat only while sk_hashed(sk) is still true,
since __x25_destroy_socket() unlinks the socket before dropping it.  Arm
the deferred destroy timer the same way and drop its reference in
x25_destroy_timer().

Reproduced on net with KASAN, with the heartbeat period shortened so the
window recurs.  With this patch the reproducer no longer triggers a
report and /proc/net/x25 drains.

Discovered by XBOW, triaged by Baul Lee <baul.lee@xbow.com>

## Which versions are affected by CVE-2026-74628?


## How do I fix CVE-2026-74628?

Apply the vendor's patch.

## Is CVE-2026-74628 being exploited?

There is no known exploitation of CVE-2026-74628 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74628 and fix it if it is affected.

What it is: CVE-2026-74628 is a critical use after free vulnerability in Linux, published on 22 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-2026-74628 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-2026-74628/ (Markdown: https://insights.sbomify.com/CVE-2026-74628/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74628
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74628
- OSV: https://osv.dev/vulnerability/CVE-2026-74628

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74628/
Summaries are generated and may contain mistakes; the official description above is the record.