CVE-2025-39737 mm/kmemleak: avoid soft lockup in __kmemleak_do_cleanup()
A soft lockup in the Linux kernel's kmemleak cleanup routine can cause a denial of service on debug kernels with specific configurations.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39737?
CVE-2025-39737 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 11 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mm/kmemleak: avoid soft lockup in __kmemleak_do_cleanup()
A soft lockup warning was observed on a relative small system x86-64 system with 16 GB of memory when running a debug kernel with kmemleak enabled.
watchdog: BUG: soft lockup - CPU#8 stuck for 33s! [kworker/8:1:134]
The test system was running a workload with hot unplug happening in parallel. Then kemleak decided to disable itself due to its inability to allocate more kmemleak objects. The debug kernel has its CONFIG_DEBUG_KMEMLEAK_MEM_POOL_SIZE set to 40,000.
The soft lockup happened in kmemleak_do_cleanup() when the existing kmemleak objects were being removed and deleted one-by-one in a loop via a workqueue. In this particular case, there are at least 40,000 objects that need to be processed and given the slowness of a debug kernel and the fact that a raw_spinlock has to be acquired and released in __delete_object(), it could take a while to properly handle all these objects.
As kmemleak has been disabled in this case, the object removal and deletion process can be further optimized as locking isn't really needed. However, it is probably not worth the effort to optimize for such an edge case that should rarely happen. So the simple solution is to call cond_resched() at periodic interval in the iteration loop to avoid soft lockup.
Weakness: CWE-401
Which versions are affected by CVE-2025-39737?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-39737?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-39737 being exploited?
There is no known exploitation of CVE-2025-39737 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-67250, AZL-75318, BELL-CVE-2025-39737, DEBIAN-CVE-2025-39737, GHSA-x37q-qw63-qf28, ROOT-OS-DEBIAN-11-CVE-2025-39737 and 3 more.