# CVE-2026-98258: posix-cpu-timers: Prevent freeing a timer which is queued on the expiry list

> A race condition in Linux kernel POSIX CPU timers allows use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-98258, DEBIAN-CVE-2026-98258, GHSA-h9hq-jmqv-hjx4, UBUNTU-CVE-2026-98258

## What is CVE-2026-98258?

CVE-2026-98258 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

posix-cpu-timers: Prevent freeing a timer which is queued on the expiry list

Kijo analyzed another race in the POSIX CPU timer code:

Commit bf635681c906 converted cpu_timer::firing from a tristate value to a
boolean. This lost the distinction between "not owned by the firing list"
and "still owned, but delivery was canceled". The resulting race is:

    expiry handler              timer_settime()        timer_delete()
    --------------              ---------------        --------------
    collect timer onto
    private firing list
    firing = true
                                observes firing = true
                                firing = false
                                return TIMER_RETRY
                                wait for handler
                                                       observes firing = false
                                                       finish deletion
                                                       unhash and free timer
    resume list traversal
    read freed elist.next
    -> UAF

The firing bit is clearly the wrong indicator since that commit.

Check whether the timer is queued on the expiry list or not instead. If it
is queued clear the firing bit to prevent signal delivery as before and
return TIMER_RETRY so the caller unlocks the timer which allows the expiry
code to make progress and remove it from the list.

## Which versions are affected by CVE-2026-98258?


## How do I fix CVE-2026-98258?

Apply the vendor's patch.

## Is CVE-2026-98258 being exploited?

There is no known exploitation of CVE-2026-98258 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98258 and fix it if it is affected.

What it is: CVE-2026-98258 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98258 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-2026-98258/ (Markdown: https://insights.sbomify.com/CVE-2026-98258/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98258
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98258
- OSV: https://osv.dev/vulnerability/CVE-2026-98258

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98258/
Summaries are generated and may contain mistakes; the official description above is the record.