# CVE-2025-39874: macsec: sync features on RTM_NEWLINK

> A race condition in the Linux kernel macsec driver can cause a deadlock when updating network features, 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:** 23 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-39874, DEBIAN-CVE-2025-39874, GHSA-rmcq-9vcc-9423, UBUNTU-CVE-2025-39874

## What is CVE-2025-39874?

CVE-2025-39874 is a medium-severity denial of service vulnerability in Linux kernel, published on 23 Sep 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:

macsec: sync features on RTM_NEWLINK

Syzkaller managed to lock the lower device via ETHTOOL_SFEATURES:

 netdev_lock include/linux/netdevice.h:2761 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 netdev_sync_lower_features net/core/dev.c:10649 [inline]
 __netdev_update_features+0xcb1/0x1be0 net/core/dev.c:10819
 netdev_update_features+0x6d/0xe0 net/core/dev.c:10876
 macsec_notify+0x2f5/0x660 drivers/net/macsec.c:4533
 notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 netdev_features_change+0x85/0xc0 net/core/dev.c:1570
 __dev_ethtool net/ethtool/ioctl.c:3469 [inline]
 dev_ethtool+0x1536/0x19b0 net/ethtool/ioctl.c:3502
 dev_ioctl+0x392/0x1150 net/core/dev_ioctl.c:759

It happens because lower features are out of sync with the upper:

  __dev_ethtool (real_dev)
    netdev_lock_ops(real_dev)
    ETHTOOL_SFEATURES
      __netdev_features_change
        netdev_sync_upper_features
          disable LRO on the lower
    if (old_features != dev->features)
      netdev_features_change
        fires NETDEV_FEAT_CHANGE
	macsec_notify
	  NETDEV_FEAT_CHANGE
	    netdev_update_features (for each macsec dev)
	      netdev_sync_lower_features
	        if (upper_features != lower_features)
	          netdev_lock_ops(lower) # lower == real_dev
		  stuck
		  ...

    netdev_unlock_ops(real_dev)

Per commit af5f54b0ef9e ("net: Lock lower level devices when updating
features"), we elide the lock/unlock when the upper and lower features
are synced. Makes sure the lower (real_dev) has proper features after
the macsec link has been created. This makes sure we never hit the
situation where we need to sync upper flags to the lower.

## Which versions are affected by CVE-2025-39874?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39874?

Apply the vendor's patch.

## Is CVE-2025-39874 being exploited?

There is no known exploitation of CVE-2025-39874 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-2025-39874 and fix it if it is affected.

What it is: CVE-2025-39874 is a medium-severity denial of service vulnerability in Linux kernel, published on 23 Sep 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-2025-39874 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-2025-39874/ (Markdown: https://insights.sbomify.com/CVE-2025-39874/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39874
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39874
- OSV: https://osv.dev/vulnerability/CVE-2025-39874

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39874/
Summaries are generated and may contain mistakes; the official description above is the record.