CVE-2025-40103 smb: client: Fix refcount leak for cifs_sb_tlink
A refcount leak in the Linux kernel SMB client allows local attackers to exhaust resources, causing 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-2025-40103?
CVE-2025-40103 is a denial of service vulnerability in Linux, published on 30 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:
smb: client: Fix refcount leak for cifs_sb_tlink
Fix three refcount inconsistency issues related to `cifs_sb_tlink`.
Comments for `cifs_sb_tlink` state that `cifs_put_tlink()` needs to be called after successful calls to `cifs_sb_tlink()`. Three calls fail to update refcount accordingly, leading to possible resource leaks.
Which versions are affected by CVE-2025-40103?
How do I fix CVE-2025-40103?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40103 being exploited?
There is no known exploitation of CVE-2025-40103 in the wild and no public exploit code.
Sources
Also known as AZL-69404, BELL-CVE-2025-40103, DEBIAN-CVE-2025-40103, GHSA-rg54-mxfq-r39j, ROOT-OS-DEBIAN-11-CVE-2025-40103, ROOT-OS-UBUNTU-2204-CVE-2025-40103 and 2 more.