CVE-2025-21942
📋 TL;DR
A race condition in the Linux kernel's BTRFS filesystem for zoned storage devices causes a deadlock when handling allocation failures. This vulnerability affects Linux systems using BTRFS with zoned storage devices, potentially causing system hangs and denial of service.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
System becomes completely unresponsive due to deadlock, requiring hard reboot and potentially causing data corruption or loss.
Likely Case
System hangs or becomes unresponsive when BTRFS operations encounter specific allocation patterns on zoned storage, leading to denial of service.
If Mitigated
Minor performance impact or temporary unavailability of affected filesystem operations.
🎯 Exploit Status
Exploitation requires local access and ability to trigger specific BTRFS operations on zoned storage. The vulnerability was discovered through fuzzing/testing (generic/751 test).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with fixes: 3fcff2f55389306482ab049b4321bda49495e546, 5a4041f2c47247575a6c2e53ce14f7b0ac946c33, 5f4863cfb29a7b4fe7625ce148d0b9000b75b802
Vendor Advisory: https://git.kernel.org/stable/c/3fcff2f55389306482ab049b4321bda49495e546
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 matches patched release.
🔧 Temporary Workarounds
Disable BTRFS zoned mode
linuxIf not using zoned storage features, disable BTRFS zoned mode to avoid the vulnerability.
# Mount BTRFS without zoned support
# Check if you're using zoned mode: cat /proc/mounts | grep btrfs
# Remount with appropriate options if needed
Use alternative filesystem
linuxTemporarily use EXT4 or XFS instead of BTRFS for zoned storage until patched.
# Backup data and reformat with alternative filesystem
# Use mkfs.ext4 or mkfs.xfs instead of mkfs.btrfs
🧯 If You Can't Patch
- Avoid using BTRFS with zoned storage devices
- Monitor system for hung tasks and restart affected services if hangs occur
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if using BTRFS with zoned storage: uname -r and check /proc/mounts for btrfs mountsCheck Version:
uname -rVerify Fix Applied:
Verify kernel version is patched: uname -r should show version containing the fix commits📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing hung tasks related to btrfs
- System becoming unresponsive with btrfs-related processes in D state
- Messages about extent locking timeouts
Network Indicators:
- None - this is a local filesystem issue
SIEM Query:
Process monitoring for btrfs processes stuck in D state for extended periods