# CVE-2025-38687: comedi: fix race between polling and detaching

> A race condition in the Linux kernel comedi driver allows a use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 4 Sep 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-66860, BELL-CVE-2025-38687, DEBIAN-CVE-2025-38687, GHSA-gmr8-hqwc-6phj, ROOT-OS-DEBIAN-11-CVE-2025-38687, ROOT-OS-DEBIAN-12-CVE-2025-38687, ROOT-OS-UBUNTU-2204-CVE-2025-38687, ROOT-OS-UBUNTU-2404-CVE-2025-38687, UBUNTU-CVE-2025-38687

## What is CVE-2025-38687?

CVE-2025-38687 is a high-severity use after free vulnerability in Debian Debian Linux, published on 4 Sep 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

comedi: fix race between polling and detaching

syzbot reports a use-after-free in comedi in the below link, which is
due to comedi gladly removing the allocated async area even though poll
requests are still active on the wait_queue_head inside of it. This can
cause a use-after-free when the poll entries are later triggered or
removed, as the memory for the wait_queue_head has been freed.  We need
to check there are no tasks queued on any of the subdevices' wait queues
before allowing the device to be detached by the `COMEDI_DEVCONFIG`
ioctl.

Tasks will read-lock `dev->attach_lock` before adding themselves to the
subdevice wait queue, so fix the problem in the `COMEDI_DEVCONFIG` ioctl
handler by write-locking `dev->attach_lock` before checking that all of
the subdevices are safe to be deleted.  This includes testing for any
sleepers on the subdevices' wait queues.  It remains locked until the
device has been detached.  This requires the `comedi_device_detach()`
function to be refactored slightly, moving the bulk of it into new
function `comedi_device_detach_locked()`.

Note that the refactor of `comedi_device_detach()` results in
`comedi_device_cancel_all()` now being called while `dev->attach_lock`
is write-locked, which wasn't the case previously, but that does not
matter.

Thanks to Jens Axboe for diagnosing the problem and co-developing this
patch.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-38687?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38687?

Apply the vendor's patch.

## Is CVE-2025-38687 being exploited?

There is no known exploitation of CVE-2025-38687 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38687 and fix it if it is affected.

What it is: CVE-2025-38687 is a high-severity use after free vulnerability in Debian Debian Linux, published on 4 Sep 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2025-38687 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-38687/ (Markdown: https://insights.sbomify.com/CVE-2025-38687/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38687
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38687
- OSV: https://osv.dev/vulnerability/CVE-2025-38687

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38687/
Summaries are generated and may contain mistakes; the official description above is the record.