# CVE-2023-53728: posix-timers: Ensure timer ID search-loop limit is valid

> A race condition in Linux kernel posix timers can cause an infinite loop, leading to denial of service for local attackers.

- **Severity:** Not scored
- **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:** 22 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53728, DEBIAN-CVE-2023-53728, GHSA-2cvf-73cf-jrw5, UBUNTU-CVE-2023-53728

## What is CVE-2023-53728?

CVE-2023-53728 is a vulnerability in Linux, published on 22 Oct 2025. 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-timers: Ensure timer ID search-loop limit is valid

posix_timer_add() tries to allocate a posix timer ID by starting from the
cached ID which was stored by the last successful allocation.

This is done in a loop searching the ID space for a free slot one by
one. The loop has to terminate when the search wrapped around to the
starting point.

But that's racy vs. establishing the starting point. That is read out
lockless, which leads to the following problem:

CPU0	  	      	     	   CPU1
posix_timer_add()
  start = sig->posix_timer_id;
  lock(hash_lock);
  ...				   posix_timer_add()
  if (++sig->posix_timer_id < 0)
      			             start = sig->posix_timer_id;
     sig->posix_timer_id = 0;

So CPU1 can observe a negative start value, i.e. -1, and the loop break
never happens because the condition can never be true:

  if (sig->posix_timer_id == start)
     break;

While this is unlikely to ever turn into an endless loop as the ID space is
huge (INT_MAX), the racy read of the start value caught the attention of
KCSAN and Dmitry unearthed that incorrectness.

Rewrite it so that all id operations are under the hash lock.

## Which versions are affected by CVE-2023-53728?


## How do I fix CVE-2023-53728?

Apply the vendor's patch.

## Is CVE-2023-53728 being exploited?

There is no known exploitation of CVE-2023-53728 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-53728 and fix it if it is affected.

What it is: CVE-2023-53728 is a vulnerability in Linux, published on 22 Oct 2025. 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-2023-53728 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-2023-53728/ (Markdown: https://insights.sbomify.com/CVE-2023-53728/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53728
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53728
- OSV: https://osv.dev/vulnerability/CVE-2023-53728

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53728/
Summaries are generated and may contain mistakes; the official description above is the record.