CVE-2025-40004 net/9p: Fix buffer overflow in USB transport layer
A malicious USB host can trigger a heap buffer overflow in the Linux kernel's 9pfs USB transport, potentially leading to code execution or privilege escalation.
- 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-2025-40004?
CVE-2025-40004 is a memory corruption vulnerability in Linux, published on 20 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:
net/9p: Fix buffer overflow in USB transport layer
A buffer overflow vulnerability exists in the USB 9pfs transport layer where inconsistent size validation between packet header parsing and actual data copying allows a malicious USB host to overflow heap buffers.
The issue occurs because: - usb9pfs_rx_header() validates only the declared size in packet header - usb9pfs_rx_complete() uses req->actual (actual received bytes) for memcpy
This allows an attacker to craft packets with small declared size (bypassing validation) but large actual payload (triggering overflow in memcpy).
Add validation in usb9pfs_rx_complete() to ensure req->actual does not exceed the buffer capacity before copying data.
Which versions are affected by CVE-2025-40004?
How do I fix CVE-2025-40004?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-40004 being exploited?
There is no known exploitation of CVE-2025-40004 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40004, DEBIAN-CVE-2025-40004, GHSA-7p6w-xg84-v7c5, ROOT-OS-DEBIAN-13-CVE-2025-40004, UBUNTU-CVE-2025-40004.