# CVE-2025-39925: can: j1939: implement NETDEV_UNREGISTER notification handler

> A missing notification handler in the Linux kernel CAN J1939 protocol causes a reference count leak, preventing network device unregistration and leading to a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 1 Oct 2025
- **Updated:** 2 Sep 2026
- **Also known as:** BELL-CVE-2025-39925, DEBIAN-CVE-2025-39925, GHSA-g35j-5v93-p28m, ROOT-OS-DEBIAN-11-CVE-2025-39925, ROOT-OS-DEBIAN-12-CVE-2025-39925, ROOT-OS-DEBIAN-13-CVE-2025-39925, ROOT-OS-UBUNTU-2204-CVE-2025-39925, ROOT-OS-UBUNTU-2404-CVE-2025-39925, UBUNTU-CVE-2025-39925

## What is CVE-2025-39925?

CVE-2025-39925 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 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:

can: j1939: implement NETDEV_UNREGISTER notification handler

syzbot is reporting

  unregister_netdevice: waiting for vcan0 to become free. Usage count = 2

problem, for j1939 protocol did not have NETDEV_UNREGISTER notification
handler for undoing changes made by j1939_sk_bind().

Commit 25fe97cb7620 ("can: j1939: move j1939_priv_put() into sk_destruct
callback") expects that a call to j1939_priv_put() can be unconditionally
delayed until j1939_sk_sock_destruct() is called. But we need to call
j1939_priv_put() against an extra ref held by j1939_sk_bind() call
(as a part of undoing changes made by j1939_sk_bind()) as soon as
NETDEV_UNREGISTER notification fires (i.e. before j1939_sk_sock_destruct()
is called via j1939_sk_release()). Otherwise, the extra ref on "struct
j1939_priv" held by j1939_sk_bind() call prevents "struct net_device" from
dropping the usage count to 1; making it impossible for
unregister_netdevice() to continue.

[mkl: remove space in front of label]

## Which versions are affected by CVE-2025-39925?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39925?

Apply the vendor's patch.

## Is CVE-2025-39925 being exploited?

There is no known exploitation of CVE-2025-39925 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39925 and fix it if it is affected.

What it is: CVE-2025-39925 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 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-2025-39925 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-39925/ (Markdown: https://insights.sbomify.com/CVE-2025-39925/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39925
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39925
- OSV: https://osv.dev/vulnerability/CVE-2025-39925

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39925/
Summaries are generated and may contain mistakes; the official description above is the record.