CVE-2025-39915 – A race condition in the Linux kernel's network ... (How to Fix)

📋 TL;DR

A race condition in the Linux kernel's network PHY subsystem could cause a deadlock when certain network events occur concurrently. This affects systems using phylink with in-band configuration, potentially causing network interface failures. The vulnerability requires specific timing conditions to trigger.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific affected versions not specified in CVE, but patches exist for stable branches

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ⚠️ Yes

Notes: Requires systems using phylink with in-band configuration; SFP modules and optical interfaces may be particularly affected.

📦 What is this software?

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel deadlock causing network interface failure, requiring system reboot to restore connectivity.

🟠

Likely Case

Intermittent network connectivity issues or interface failures during network reconfiguration events.

🟢

If Mitigated

Minimal impact if proper kernel locking order is maintained and race conditions are avoided.

🌐 Internet-Facing: LOW - Requires local access or specific network conditions to trigger, not directly exploitable from remote.

🏢 Internal Only: MEDIUM - Could affect critical network infrastructure and cause service disruption if triggered.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: HIGH - Requires specific timing and race conditions to trigger deadlock

Discovered via lockdep analysis; exploitation requires concurrent network state changes.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Patches available in stable kernel trees (commits 052ac41c379c8b87629808be612a482b2d0ae283 and e2a10daba84968f6b5777d150985fd7d6abc9c84)

Vendor Advisory: https://git.kernel.org/stable/c/052ac41c379c8b87629808be612a482b2d0ae283

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version
2. Apply specific commits if backporting
3. Reboot system to load new kernel

🔧 Temporary Workarounds

Avoid concurrent network configuration

linux

Minimize network interface reconfiguration events that could trigger the race condition

🧯 If You Can't Patch

Monitor network interfaces for unexpected failures
Implement network redundancy to mitigate single interface failures

🔍 How to Verify

Check if Vulnerable:

Check kernel version and if using phylink with in-band configuration

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version includes the fix commits or check for absence of lockdep warnings related to phy/phylink locking

📡 Detection & Monitoring

Log Indicators:

Kernel lockdep warnings
Network interface failure logs
System hang or deadlock indicators

Network Indicators:

Unexpected network interface failures
Intermittent connectivity issues

SIEM Query:

Search for kernel logs containing 'possible circular locking dependency' or 'deadlock' related to phy/phylink

📊 Metadata

CVE ID: CVE-2025-39915

CVSS v3 Score: 5.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-667

EPSS Score: 0.02% exploit probability (4.5th percentile)

Published: October 1, 2025

Last Updated: January 14, 2026

🔗 References

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