CVE-2025-21896
📋 TL;DR
A use-after-free vulnerability in the Linux kernel's FUSE filesystem implementation allows attackers to potentially crash the kernel or execute arbitrary code. This affects systems using FUSE filesystems with readahead functionality enabled. 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash or potential privilege escalation to kernel-level code execution.
Likely Case
Kernel crash causing system instability or denial of service.
If Mitigated
No impact if FUSE filesystems are not in use or readahead is disabled.
🎯 Exploit Status
Requires local access and ability to mount/access FUSE filesystems. Exploit would need to trigger specific readahead and splice operations.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits 0c67c37e1710b2a8f61c8a02db95a51fe577e2c1 or 60db11f1b7fba4a66b117ea998d965818784a98d
Vendor Advisory: https://git.kernel.org/stable/c/0c67c37e1710b2a8f61c8a02db95a51fe577e2c1
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
Disable FUSE readahead
linuxDisable readahead functionality for FUSE filesystems
echo 0 > /sys/fs/fuse/readahead_max
Unmount FUSE filesystems
linuxRemove FUSE mounts if not required
umount /path/to/fuse/mount
🧯 If You Can't Patch
- Restrict user access to prevent mounting FUSE filesystems
- Implement strict access controls and monitoring on systems with FUSE mounts
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if FUSE is in use: 'uname -r' and 'mount | grep fuse'Check Version:
uname -rVerify Fix Applied:
Verify kernel version is after fix commits and test FUSE functionality📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- FUSE-related crash dumps
- System instability after FUSE operations
Network Indicators:
- None - local vulnerability only
SIEM Query:
search for kernel panic events or FUSE-related errors in system logs