# CVE-2025-39905: net: phylink: add lock for serializing concurrent pl->phydev writes with resolver

> A race condition in the Linux kernel's phylink subsystem can lead to system instability or denial of service due to unsynchronized access to phydev pointers.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/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:** 1 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-68040, AZL-72358, BELL-CVE-2025-39905, DEBIAN-CVE-2025-39905, GHSA-3w4m-c8rq-62jj, ROOT-OS-DEBIAN-11-CVE-2025-39905, ROOT-OS-DEBIAN-12-CVE-2025-39905, ROOT-OS-DEBIAN-13-CVE-2025-39905, ROOT-OS-UBUNTU-2204-CVE-2025-39905, ROOT-OS-UBUNTU-2404-CVE-2025-39905, UBUNTU-CVE-2025-39905

## What is CVE-2025-39905?

CVE-2025-39905 is a high-severity 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:

net: phylink: add lock for serializing concurrent pl->phydev writes with resolver

Currently phylink_resolve() protects itself against concurrent
phylink_bringup_phy() or phylink_disconnect_phy() calls which modify
pl->phydev by relying on pl->state_mutex.

The problem is that in phylink_resolve(), pl->state_mutex is in a lock
inversion state with pl->phydev->lock. So pl->phydev->lock needs to be
acquired prior to pl->state_mutex. But that requires dereferencing
pl->phydev in the first place, and without pl->state_mutex, that is
racy.

Hence the reason for the extra lock. Currently it is redundant, but it
will serve a functional purpose once mutex_lock(&phy->lock) will be
moved outside of the mutex_lock(&pl->state_mutex) section.

Another alternative considered would have been to let phylink_resolve()
acquire the rtnl_mutex, which is also held when phylink_bringup_phy()
and phylink_disconnect_phy() are called. But since phylink_disconnect_phy()
runs under rtnl_lock(), it would deadlock with phylink_resolve() when
calling flush_work(&pl->resolve). Additionally, it would have been
undesirable because it would have unnecessarily blocked many other call
paths as well in the entire kernel, so the smaller-scoped lock was
preferred.

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

## Which versions are affected by CVE-2025-39905?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39905?

Apply the vendor's patch.

## Is CVE-2025-39905 being exploited?

There is no known exploitation of CVE-2025-39905 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-2025-39905 and fix it if it is affected.

What it is: CVE-2025-39905 is a high-severity 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-2025-39905 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-2025-39905/ (Markdown: https://insights.sbomify.com/CVE-2025-39905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39905
- OSV: https://osv.dev/vulnerability/CVE-2025-39905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39905/
Summaries are generated and may contain mistakes; the official description above is the record.