# CVE-2025-40249: gpio: cdev: make sure the cdev fd is still active before emitting events

> A use-after-free vulnerability in the Linux kernel GPIO subsystem allows attackers to cause denial of service or potentially execute code via race conditions during file descriptor release.

- **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:** 4 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40249, DEBIAN-CVE-2025-40249, GHSA-p8p4-x362-gp65, UBUNTU-CVE-2025-40249

## What is CVE-2025-40249?

CVE-2025-40249 is a high-severity use after free vulnerability in Linux, published on 4 Dec 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:

gpio: cdev: make sure the cdev fd is still active before emitting events

With the final call to fput() on a file descriptor, the release action
may be deferred and scheduled on a work queue. The reference count of
that descriptor is still zero and it must not be used. It's possible
that a GPIO change, we want to notify the user-space about, happens
AFTER the reference count on the file descriptor associated with the
character device went down to zero but BEFORE the .release() callback
was called from the workqueue and so BEFORE we unregistered from the
notifier.

Using the regular get_file() routine in this situation triggers the
following warning:

  struct file::f_count incremented from zero; use-after-free condition present!

So use the get_file_active() variant that will return NULL on file
descriptors that have been or are being released.

## Which versions are affected by CVE-2025-40249?


## How do I fix CVE-2025-40249?

Apply the vendor's patch.

## Is CVE-2025-40249 being exploited?

There is no known exploitation of CVE-2025-40249 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40249 and fix it if it is affected.

What it is: CVE-2025-40249 is a high-severity use after free vulnerability in Linux, published on 4 Dec 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-2025-40249 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-2025-40249/ (Markdown: https://insights.sbomify.com/CVE-2025-40249/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40249
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40249
- OSV: https://osv.dev/vulnerability/CVE-2025-40249

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40249/
Summaries are generated and may contain mistakes; the official description above is the record.