CVE-2025-40249 gpio: cdev: make sure the cdev fd is still active before emitting events
A use-after-free vulnerability in the Linux kernel GPIO subsystem allows attackers to cause denial of service or potentially execute code via race conditions during file descriptor release.
- 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-2025-40249?
CVE-2025-40249 is a high-severity use after free vulnerability in Linux, published on 4 Dec 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:
gpio: cdev: make sure the cdev fd is still active before emitting events
With the final call to fput() on a file descriptor, the release action may be deferred and scheduled on a work queue. The reference count of that descriptor is still zero and it must not be used. It's possible that a GPIO change, we want to notify the user-space about, happens AFTER the reference count on the file descriptor associated with the character device went down to zero but BEFORE the .release() callback was called from the workqueue and so BEFORE we unregistered from the notifier.
Using the regular get_file() routine in this situation triggers the following warning:
struct file::f_count incremented from zero; use-after-free condition present!
So use the get_file_active() variant that will return NULL on file descriptors that have been or are being released.
Which versions are affected by CVE-2025-40249?
How do I fix CVE-2025-40249?
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-2025-40249 being exploited?
There is no known exploitation of CVE-2025-40249 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40249, DEBIAN-CVE-2025-40249, GHSA-p8p4-x362-gp65, UBUNTU-CVE-2025-40249.