CVE-2025-38242
📋 TL;DR
A race condition vulnerability in the Linux kernel's userfaultfd subsystem allows incorrect memory page handling during swap operations. This can lead to memory accounting corruption and potential system instability. Systems running vulnerable Linux kernel versions with userfaultfd enabled are affected.
💻 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
System crash or kernel panic due to memory corruption, potentially leading to denial of service and data loss.
Likely Case
Memory accounting errors causing system instability, performance degradation, or application crashes.
If Mitigated
Minimal impact if userfaultfd is disabled or systems are properly patched.
🎯 Exploit Status
Exploitation requires local access, specific timing conditions, and userfaultfd to be enabled. The race window is very narrow.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits 0ea148a799198518d8ebab63ddd0bb6114a103bc, 4c443046d8c9ed8724a4f4c3c2457d3ac8814b2f, and db2ca8074955ca64187a4fb596dd290b9c446cd3
Vendor Advisory: https://git.kernel.org/stable/c/0ea148a799198518d8ebab63ddd0bb6114a103bc
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version matches patched release.
🔧 Temporary Workarounds
Disable userfaultfd
linuxDisable the userfaultfd subsystem if not required
echo 0 > /proc/sys/vm/unprivileged_userfaultfd
sysctl -w vm.unprivileged_userfaultfd=0
Restrict userfaultfd access
linuxLimit userfaultfd usage to privileged users only
sysctl -w vm.userfaultfd_restricted=1
🧯 If You Can't Patch
- Disable userfaultfd subsystem completely via kernel boot parameters
- Implement strict access controls to prevent unprivileged users from using userfaultfd
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if userfaultfd is enabled: cat /proc/sys/vm/unprivileged_userfaultfdCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes the fix commits and userfaultfd restrictions are in place📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- BUG: Bad rss-counter state errors in dmesg
- Memory accounting corruption warnings
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND ("Bad rss-counter state" OR "userfaultfd_move" OR "MM_ANONPAGES")