CVE-2025-39876
📋 TL;DR
A NULL pointer dereference vulnerability in the Linux kernel's FEC (Fast Ethernet Controller) driver could cause kernel panic and system crashes when the of_phy_find_device function returns NULL. This affects Linux systems using the FEC network driver, particularly embedded devices and IoT systems. The vulnerability requires local access to trigger.
💻 Affected Systems
- Linux kernel with FEC network driver enabled
📦 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 →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 →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 panic leading to system crash and denial of service, potentially requiring physical reboot of affected devices.
Likely Case
System instability or crash when network interface operations trigger the vulnerable code path, causing temporary service disruption.
If Mitigated
Minimal impact with proper access controls preventing unauthorized local users from triggering the vulnerable code.
🎯 Exploit Status
Requires local access and ability to trigger specific network driver operations; not trivial to exploit remotely
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in stable kernel trees (see references)
Vendor Advisory: https://git.kernel.org/stable/c/03e79de4608bdd48ad6eec272e196124cefaf798
Restart Required: Yes
Instructions:
1. Update to patched kernel version from your distribution's repository. 2. Rebuild kernel if using custom kernel. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable FEC driver if not needed
LinuxRemove or blacklist the FEC network driver module if not required for system operation
echo 'blacklist fec' >> /etc/modprobe.d/blacklist-fec.conf
update-initramfs -u
reboot
🧯 If You Can't Patch
- Restrict local user access to prevent unauthorized users from triggering vulnerable code paths
- Implement monitoring for kernel panic events and system crashes related to network operations
🔍 How to Verify
Check if Vulnerable:
Check if FEC driver is loaded: lsmod | grep fec_enet; check kernel version against patched versionsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version is updated to patched version and FEC driver loads without issues📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/kern.log or dmesg
- System crash reports related to network operations
Network Indicators:
- Sudden loss of network connectivity on FEC interfaces
- System reboots without apparent cause
SIEM Query:
source="kernel" AND ("panic" OR "Oops") AND ("fec" OR "phy")🔗 References
- https://git.kernel.org/stable/c/03e79de4608bdd48ad6eec272e196124cefaf798
- https://git.kernel.org/stable/c/20a3433d31c2d2bf70ab0abec75f3136b42ae66c
- https://git.kernel.org/stable/c/4fe53aaa4271a72fe5fe3e88a45ce01646b68dc5
- https://git.kernel.org/stable/c/5f1bb554a131e59b28482abad21f691390651752
- https://git.kernel.org/stable/c/8c60d12bba14dc655d2d948b1dbf390b3ae39cb8
- https://git.kernel.org/stable/c/93a699d6e92cfdfa9eb9dbb8c653b5322542ca4f
- https://git.kernel.org/stable/c/eb148d85e126c47d65be34f2a465d69432ca5541
- https://git.kernel.org/stable/c/fe78891f296ac05bf4e5295c9829ef822f3c32e7
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
