CVE-2025-40084 ksmbd: transport_ipc: validate payload size before reading handle
A missing size check in the Linux kernel ksmbd module allows a local attacker to trigger a 4-byte out-of-bounds read, potentially causing a system crash.
- 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-2025-40084?
CVE-2025-40084 is a high-severity vulnerability in Linux, published on 29 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:
ksmbd: transport_ipc: validate payload size before reading handle
handle_response() dereferences the payload as a 4-byte handle without verifying that the declared payload size is at least 4 bytes. A malformed or truncated message from ksmbd.mountd can lead to a 4-byte read past the declared payload size. Validate the size before dereferencing.
This is a minimal fix to guard the initial handle read.
Which versions are affected by CVE-2025-40084?
How do I fix CVE-2025-40084?
Apply the vendor's patch.
Is CVE-2025-40084 being exploited?
There is no known exploitation of CVE-2025-40084 in the wild and no public exploit code.
Sources
Also known as AZL-69024, BELL-CVE-2025-40084, DEBIAN-CVE-2025-40084, GHSA-pxm9-5xjv-gw34, ROOT-OS-DEBIAN-11-CVE-2025-40084, ROOT-OS-DEBIAN-12-CVE-2025-40084 and 4 more.