CVE-2025-39884
📋 TL;DR
A race condition in the Linux kernel's Btrfs filesystem can cause subvolume deletion to hang indefinitely, leading to system soft lockups. This affects Linux systems using Btrfs filesystem with subvolumes. The vulnerability requires local access to trigger.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
System soft lockup requiring hard reboot, causing denial of service and potential data corruption in Btrfs filesystem operations.
Likely Case
Subvolume deletion operations hang, requiring manual intervention to kill processes or reboot the system.
If Mitigated
Minor performance impact during inode operations with no functional disruption.
🎯 Exploit Status
Requires local access and timing race condition between inode eviction and caching operations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits 9ba898c9fcbe6ebb88bcd4df8aab0f90090d202e, f1498abaf74f8d7b1e7001f16ed77818d8ae6a59, or f6a6c280059c4ddc23e12e3de1b01098e240036f
Vendor Advisory: https://git.kernel.org/stable/c/9ba898c9fcbe6ebb88bcd4df8aab0f90090d202e
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Avoid Btrfs subvolume deletion
allTemporarily avoid deleting Btrfs subvolumes until patched.
Use alternative filesystem
allConsider using ext4 or xfs for critical systems until patched.
🧯 If You Can't Patch
- Monitor system for soft lockups and hung subvolume deletion operations
- Implement strict access controls to limit who can perform Btrfs subvolume operations
🔍 How to Verify
Check if Vulnerable:
Check kernel version and verify if Btrfs is in use: 'uname -r' and 'mount | grep btrfs'Check Version:
uname -rVerify Fix Applied:
Verify kernel version contains the fix commits: 'uname -r' and check with distribution's package manager📡 Detection & Monitoring
Log Indicators:
- Kernel soft lockup messages in dmesg
- Hung subvolume deletion processes in system logs
Network Indicators:
- None - local filesystem issue
SIEM Query:
search 'soft lockup' OR 'hung task' AND 'btrfs' in kernel logs