CVE-2025-39916
📋 TL;DR
A divide-by-zero vulnerability in the Linux kernel's DAMON_RECLAIM subsystem can cause kernel crashes when creating new memory reclamation schemes. This affects Linux systems using DAMON_RECLAIM for proactive memory management. 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 →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 privileged users or processes attempt to configure DAMON_RECLAIM with invalid parameters.
If Mitigated
System remains stable as the patch returns -EINVAL error instead of crashing, allowing graceful error handling.
🎯 Exploit Status
Exploitation requires local access and ability to configure DAMON_RECLAIM parameters.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions containing commits: 40cb9b38b645, 5d6eeb3c683c, 64dc351e5827, 9fe0415156fb, e6b543ca9806
Vendor Advisory: https://git.kernel.org/stable/c/40cb9b38b645126fdd1d6aa3d6811a8ad50ddfa1
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Disable DAMON_RECLAIM
linuxPrevent exploitation by disabling the DAMON_RECLAIM subsystem
echo '0' > /sys/kernel/mm/damon/reclaim/enabled
Restrict access to DAMON_RECLAIM controls
linuxLimit which users can access DAMON_RECLAIM configuration interfaces
chmod 600 /sys/kernel/mm/damon/reclaim/*
set appropriate SELinux/AppArmor policies
🧯 If You Can't Patch
- Disable DAMON_RECLAIM feature if not required
- Implement strict access controls to prevent unauthorized users from configuring DAMON_RECLAIM
🔍 How to Verify
Check if Vulnerable:
Check if DAMON_RECLAIM is enabled and kernel version is vulnerable: cat /sys/kernel/mm/damon/reclaim/enabled && uname -rCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits and test creating DAMON_RECLAIM schemes with zero aggr_interval📡 Detection & Monitoring
Log Indicators:
- Kernel panic logs
- Divide-by-zero errors in kernel logs
- System crash/reboot events
Network Indicators:
- None - local vulnerability only
SIEM Query:
source="kernel" AND ("divide by zero" OR "panic" OR "oops") AND "damon_reclaim"🔗 References
- https://git.kernel.org/stable/c/40cb9b38b645126fdd1d6aa3d6811a8ad50ddfa1
- https://git.kernel.org/stable/c/5d6eeb3c683c777ed4538eb3a650bb7da17a7cff
- https://git.kernel.org/stable/c/64dc351e58271c1e9005e42f5216b4f3d7a39b66
- https://git.kernel.org/stable/c/9fe0415156fbde773b31f920201cb70b1f0e40fe
- https://git.kernel.org/stable/c/e6b543ca9806d7bced863f43020e016ee996c057
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
