CVE-2025-39866
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's __mark_inode_dirty() function allows attackers to potentially crash the system or execute arbitrary code with kernel privileges. This affects Linux systems running vulnerable kernel versions, particularly those with writeback operations. The vulnerability requires local access to exploit.
💻 Affected Systems
- Linux Kernel
📦 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash or arbitrary code execution with kernel privileges, potentially resulting in complete system compromise.
Likely Case
System crash or kernel panic causing denial of service, requiring system reboot to restore functionality.
If Mitigated
Limited impact if proper access controls prevent unauthorized local users from triggering the race condition.
🎯 Exploit Status
Exploitation requires local access and ability to trigger specific race condition timing, making it challenging but possible for skilled attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in kernel commits: 1edc2feb9c759a9883dfe81cb5ed231412d8b2e4, b187c976111960e6e54a6b1fff724f6e3d39406c, bf89b1f87c72df79cf76203f71fbf8349cd5c9de, c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a, d02d2c98d25793902f65803ab853b592c7a96b29
Vendor Advisory: https://git.kernel.org/stable/c/1edc2feb9c759a9883dfe81cb5ed231412d8b2e4
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Restrict local user access
linuxLimit local user accounts and restrict permissions to reduce attack surface.
🧯 If You Can't Patch
- Implement strict access controls to limit local user accounts and privileges
- Monitor system logs for kernel panics or unusual writeback activity
🔍 How to Verify
Check if Vulnerable:
Check kernel version and compare with patched versions from kernel git commits. Vulnerable if running affected kernel versions with unpatched writeback code.Check Version:
uname -rVerify Fix Applied:
Check kernel version after update matches patched versions. Monitor system stability and absence of related kernel panics.📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- Use-after-free warnings in kernel logs
- System crashes related to writeback operations
Network Indicators:
- None - local vulnerability only
SIEM Query:
Search for kernel panic events or use-after-free warnings in system logs🔗 References
- https://git.kernel.org/stable/c/1edc2feb9c759a9883dfe81cb5ed231412d8b2e4
- https://git.kernel.org/stable/c/b187c976111960e6e54a6b1fff724f6e3d39406c
- https://git.kernel.org/stable/c/bf89b1f87c72df79cf76203f71fbf8349cd5c9de
- https://git.kernel.org/stable/c/c8c14adf80bd1a6e4a1d7ee9c2a816881c26d17a
- https://git.kernel.org/stable/c/d02d2c98d25793902f65803ab853b592c7a96b29
- https://git.kernel.org/stable/c/e2a14bbae5d8bacaa301362744a110e2be40a3a3
- https://git.kernel.org/stable/c/e63052921f1b25a836feb1500b841bff7a4a0456
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
