CVE-2025-39941 zram: fix slot write race condition
A race condition in the Linux kernel zram driver allows concurrent writes to leak memory, potentially leading to denial of service.
- 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-2025-39941?
CVE-2025-39941 is a high-severity vulnerability in Linux kernel, published on 4 Oct 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:
zram: fix slot write race condition
Parallel concurrent writes to the same zram index result in leaked zsmalloc handles. Schematically we can have something like this:
CPU0 CPU1 zram_slot_lock() zs_free(handle) zram_slot_lock() zram_slot_lock() zs_free(handle) zram_slot_lock()
compress compress handle = zs_malloc() handle = zs_malloc() zram_slot_lock zram_set_handle(handle) zram_slot_lock zram_slot_lock zram_set_handle(handle) zram_slot_lock
Either CPU0 or CPU1 zsmalloc handle will leak because zs_free() is done too early. In fact, we need to reset zram entry right before we set its new handle, all under the same slot lock scope.
Weakness: CWE-362
Which versions are affected by CVE-2025-39941?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39941?
Apply the vendor's patch.
Is CVE-2025-39941 being exploited?
There is no known exploitation of CVE-2025-39941 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39941, DEBIAN-CVE-2025-39941, GHSA-mjg7-65xv-hcjw, UBUNTU-CVE-2025-39941.