# CVE-2025-37949: xenbus: Use kref to track req lifetime

> A race condition in the Linux kernel xenbus driver causes a NULL pointer dereference, leading to a system crash.

- **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:** 20 May 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-37949, DEBIAN-CVE-2025-37949, GHSA-v8mr-frx6-j364, ROOT-OS-DEBIAN-11-CVE-2025-37949, ROOT-OS-DEBIAN-12-CVE-2025-37949, ROOT-OS-UBUNTU-2204-CVE-2025-37949, ROOT-OS-UBUNTU-2404-CVE-2025-37949, UBUNTU-CVE-2025-37949

## What is CVE-2025-37949?

CVE-2025-37949 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 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:

xenbus: Use kref to track req lifetime

Marek reported seeing a NULL pointer fault in the xenbus_thread
callstack:
BUG: kernel NULL pointer dereference, address: 0000000000000000
RIP: e030:__wake_up_common+0x4c/0x180
Call Trace:
 <TASK>
 __wake_up_common_lock+0x82/0xd0
 process_msg+0x18e/0x2f0
 xenbus_thread+0x165/0x1c0

process_msg+0x18e is req->cb(req).  req->cb is set to xs_wake_up(), a
thin wrapper around wake_up(), or xenbus_dev_queue_reply().  It seems
like it was xs_wake_up() in this case.

It seems like req may have woken up the xs_wait_for_reply(), which
kfree()ed the req.  When xenbus_thread resumes, it faults on the zero-ed
data.

Linux Device Drivers 2nd edition states:
"Normally, a wake_up call can cause an immediate reschedule to happen,
meaning that other processes might run before wake_up returns."
... which would match the behaviour observed.

Change to keeping two krefs on each request.  One for the caller, and
one for xenbus_thread.  Each will kref_put() when finished, and the last
will free it.

This use of kref matches the description in
Documentation/core-api/kref.rst

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-37949?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37949?

Apply the vendor's patch.

## Is CVE-2025-37949 being exploited?

There is no known exploitation of CVE-2025-37949 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)
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- [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-2025-37949 and fix it if it is affected.

What it is: CVE-2025-37949 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 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-2025-37949 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-2025-37949/ (Markdown: https://insights.sbomify.com/CVE-2025-37949/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37949
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37949
- OSV: https://osv.dev/vulnerability/CVE-2025-37949

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37949/
Summaries are generated and may contain mistakes; the official description above is the record.