CVE-2025-40223 most: usb: Fix use-after-free in hdm_disconnect
A use-after-free vulnerability in the Linux kernel's MOST USB driver allows local attackers to cause denial of service or potentially execute code via device disconnection.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40223?
CVE-2025-40223 is an 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:
most: usb: Fix use-after-free in hdm_disconnect
hdm_disconnect() calls most_deregister_interface(), which eventually unregisters the MOST interface device with device_unregister(iface->dev). If that drops the last reference, the device core may call release_mdev() immediately while hdm_disconnect() is still executing.
The old code also freed several mdev-owned allocations in hdm_disconnect() and then performed additional put_device() calls. Depending on refcount order, this could lead to use-after-free or double-free when release_mdev() ran (or when unregister paths also performed puts).
Fix by moving the frees of mdev-owned allocations into release_mdev(), so they happen exactly once when the device is truly released, and by dropping the extra put_device() calls in hdm_disconnect() that are redundant after device_unregister() and most_deregister_interface().
This addresses the KASAN slab-use-after-free reported by syzbot in hdm_disconnect(). See report and stack traces in the bug link below.
Which versions are affected by CVE-2025-40223?
How do I fix CVE-2025-40223?
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-2025-40223 being exploited?
There is no known exploitation of CVE-2025-40223 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40223, DEBIAN-CVE-2025-40223, GHSA-jh7w-53hp-qjqh, ROOT-OS-DEBIAN-11-CVE-2025-40223, ROOT-OS-UBUNTU-2404-CVE-2025-40223, UBUNTU-CVE-2025-40223.