CVE-2025-40328 smb: client: fix potential UAF in smb2_close_cached_fid()
A use-after-free vulnerability in the Linux kernel SMB client allows attackers to potentially execute code or escalate privileges via race conditions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2025-40328?
CVE-2025-40328 is a high-severity use after free vulnerability in Linux, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix potential UAF in smb2_close_cached_fid()
find_or_create_cached_dir() could grab a new reference after kref_put() had seen the refcount drop to zero but before cfid_list_lock is acquired in smb2_close_cached_fid(), leading to use-after-free.
Switch to kref_put_lock() so cfid_release() is called with cfid_list_lock held, closing that gap.
Which versions are affected by CVE-2025-40328?
How do I fix CVE-2025-40328?
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-2025-40328 being exploited?
There is no known exploitation of CVE-2025-40328 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40328, DEBIAN-CVE-2025-40328, GHSA-f255-x52r-mjq5, ROOT-OS-DEBIAN-12-CVE-2025-40328, ROOT-OS-DEBIAN-13-CVE-2025-40328, ROOT-OS-UBUNTU-2404-CVE-2025-40328 and 1 more.