CVE-2025-39877 mm/damon/sysfs: fix use-after-free in state_show()
A use-after-free race condition in the Linux kernel DAMON sysfs interface allows attackers to potentially execute code or escalate privileges.
- 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-2025-39877?
CVE-2025-39877 is a high-severity use after free vulnerability in Debian Debian Linux, published on 23 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/damon/sysfs: fix use-after-free in state_show()
state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race:
CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */
(The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.)
Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show().
The bug has existed since state_show() first accessed kdamond->damon_ctx.
Weakness: CWE-416
Which versions are affected by CVE-2025-39877?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-39877?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2025-39877 being exploited?
There is no known exploitation of CVE-2025-39877 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2025-39877, DEBIAN-CVE-2025-39877, GHSA-46f8-9r54-mw7h, ROOT-OS-UBUNTU-2204-CVE-2025-39877, ROOT-OS-UBUNTU-2404-CVE-2025-39877, UBUNTU-CVE-2025-39877.