CVE-2025-39916

What it actually does

Division by zero in damon_reclaim_apply_parameters when user-supplied DAMON reclaim parameters evaluate to a zero divisor, triggering a kernel oops or panic.

Why it matters to the business

Local users or container workloads can cause Linux systems to crash or become unresponsive, leading to service outages and requiring manual restarts or reboots.

How an attack unfolds

An attacker with local access supplies crafted DAMON reclaim configuration values that result in a zero divisor during parameter application, causing the kernel to fault and halt the system.

How to fix it

Update the Linux kernel to the commit 64dc351e58271c1e9005e42f5216b4f3d7a39b66 or later stable releases that contain the division guard; rebuild and deploy the patched kernel across all affected hosts.

How to confirm the fix worked

Verify the running kernel contains commit 64dc351e58271c1e9005e42f5216b4f3d7a39b66 by inspecting /proc/version or kernel build logs, then test that zero-divisor DAMON reclaim configurations no longer cause oops.

Typical attack path

1. Obtain local execution context on a Linux system running an affected kernel
2. Configure or modify DAMON reclaim parameters via sysfs or debugfs interfaces
3. Supply values that produce a zero divisor during damon_reclaim_apply_parameters
4. Trigger the parameter application path to induce divide-by-zero fault

How to detect it

Search kernel logs for oops or panic messages containing damon_reclaim_apply_parameters and division-by-zero faults; review audit logs for unusual DAMON sysfs writes by non-root processes.

What your security team should do

• Prioritize kernel upgrades on all systems exposing DAMON reclaim interfaces
• Restrict unprivileged access to DAMON sysfs/debugfs nodes until patched
• Monitor for kernel oops reports referencing damon_reclaim_apply_parameters
• Apply the fix within standard change windows given low EPSS and absence from KEV