CVE-2025-21786
📋 TL;DR
This Linux kernel vulnerability is a use-after-free bug in the workqueue subsystem that occurs when detaching rescuers from pools. It allows local attackers to potentially crash the system or execute arbitrary code with kernel privileges. All Linux systems using affected kernel versions are vulnerable.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Local privilege escalation to root, kernel panic causing system crash, or arbitrary code execution in kernel context leading to complete system compromise.
Likely Case
Kernel panic leading to system crash and denial of service, requiring physical or remote console access to reboot.
If Mitigated
Limited impact if proper access controls prevent local user access or if systems are regularly patched.
🎯 Exploit Status
Requires local access and knowledge of kernel exploitation techniques. No public exploit code identified at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits 835b69c868f53f959d4986bbecd561ba6f38e492, e76946110137703c16423baf6ee177b751a34b7e, or e7c16028a424dd35be1064a68fa318be4359310f applied
Vendor Advisory: https://git.kernel.org/stable/c/835b69c868f53f959d4986bbecd561ba6f38e492
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
allLimit local shell access to trusted users only to reduce attack surface
# Review /etc/passwd and /etc/shadow for unnecessary accounts
# Use sudo policies to restrict privileged access
🧯 If You Can't Patch
- Implement strict access controls to prevent untrusted local users from accessing the system
- Monitor for kernel panic events and unauthorized privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check kernel version and compare with distribution's security advisories for CVE-2025-21786Check Version:
uname -rVerify Fix Applied:
Verify kernel version after update matches patched version from distribution security advisory📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/messages or journalctl
- Unexpected system reboots
- Privilege escalation attempts in audit logs
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
Search for: 'kernel panic' OR 'segfault' OR 'use-after-free' in kernel logs