CVE-2025-39887
📋 TL;DR
A NULL pointer dereference vulnerability in the Linux kernel's tracing/osnoise subsystem allows local users to crash the kernel by writing malformed data to the /sys/kernel/debug/tracing/osnoise/cpus file. This affects Linux systems with kernel tracing enabled and requires local access to trigger. The vulnerability can cause denial of service through kernel panic.
💻 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
Kernel panic leading to system crash and denial of service, potentially causing data loss or service disruption.
Likely Case
Local denial of service through kernel crash when a malicious user with appropriate permissions writes to the vulnerable interface.
If Mitigated
No impact if proper access controls prevent unauthorized users from writing to debugfs or if the tracing subsystem is disabled.
🎯 Exploit Status
Proof of concept code is included in the CVE description. Exploitation requires write access to /sys/kernel/debug/tracing/osnoise/cpus.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Patched in kernel commits c1628c00c4351dd0727ef7f670694f68d9e663d8 and e33228a2cc7ff706ca88533464e8a3b525b961ed
Vendor Advisory: https://git.kernel.org/stable/c/c1628c00c4351dd0727ef7f670694f68d9e663d8
Restart Required: Yes
Instructions:
1. Update to a kernel version containing the fix. 2. Check your distribution's security advisories for patched kernel packages. 3. Reboot the system after kernel update.
🔧 Temporary Workarounds
Disable debugfs access
LinuxRestrict access to debugfs to prevent unauthorized users from triggering the vulnerability
chmod 700 /sys/kernel/debug
mount -o remount,noexec,nosuid,nodev /sys/kernel/debug
Disable osnoise tracer
LinuxDisable the vulnerable tracing subsystem
echo 0 > /sys/kernel/debug/tracing/osnoise/events/enable
🧯 If You Can't Patch
- Implement strict access controls on /sys/kernel/debug to prevent unauthorized users from writing to tracing interfaces
- Disable the osnoise tracer module if not required for system operation
🔍 How to Verify
Check if Vulnerable:
Check if /sys/kernel/debug/tracing/osnoise/cpus exists and is writable, and verify kernel version is within affected rangeCheck Version:
uname -rVerify Fix Applied:
Check kernel version against patched versions, or test the PoC to confirm system doesn't crash📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages
- NULL pointer dereference errors in kernel logs
- BUG: kernel NULL pointer dereference at bitmap_parselist
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND "NULL pointer dereference" AND "bitmap_parselist"