CVE-2025-21769
📋 TL;DR
This CVE describes a missing .owner field in the vmclock_miscdev_fops structure in the Linux kernel's PTP subsystem. When the module is unloaded while /dev/vmclock0 is open, it can cause a kernel oops (crash). This affects Linux systems using the vmclock PTP driver.
💻 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 →⚠️ Risk & Real-World Impact
Worst Case
Kernel panic leading to system crash and denial of service, potentially requiring physical access to reboot the system.
Likely Case
System instability or crash when the vmclock module is unloaded while the device file is in use, causing temporary denial of service.
If Mitigated
No impact if the vmclock module is not loaded or if proper module management prevents unloading while device is open.
🎯 Exploit Status
Exploitation requires local access and specific conditions: vmclock module loaded, /dev/vmclock0 open, and module unloading triggered.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patches available in kernel commits 3b5709225b43ee33e1026dd1fc0949a7f19b5289 and 7b07b040257c1b658ef3eca86e4b6ae02d65069c
Vendor Advisory: https://git.kernel.org/stable/c/3b5709225b43ee33e1026dd1fc0949a7f19b5289
Restart Required: Yes
Instructions:
1. Update to a patched kernel version from your distribution vendor. 2. Reboot the system to load the new kernel.
🔧 Temporary Workarounds
Prevent vmclock module unloading
linuxSet the module to prevent unloading while in use
echo 1 > /sys/module/vmclock/parameters/refcnt
Unload vmclock module if not needed
linuxRemove the vulnerable module if PTP vmclock functionality is not required
rmmod vmclock
🧯 If You Can't Patch
- Ensure vmclock module is not loaded if not needed
- Implement strict access controls to prevent unauthorized users from loading/unloading kernel modules
🔍 How to Verify
Check if Vulnerable:
Check if vmclock module is loaded: lsmod | grep vmclockCheck Version:
uname -rVerify Fix Applied:
Check kernel version against patched versions from your distribution vendor📡 Detection & Monitoring
Log Indicators:
- Kernel oops messages in /var/log/kern.log or dmesg output
- System crash/panic logs
Network Indicators:
- None - this is a local vulnerability
SIEM Query:
Search for 'kernel: Oops' or 'kernel: BUG' in system logs when vmclock module is loaded