CVE-2025-40004: net/9p: Fix buffer overflow in USB transport layer

Vulnerability summary

CVE-2025-40004 is a vulnerability in linux with no CVSS score yet. EPSS estimates a 0.27% chance of exploitation in the next 30 days, higher than 18.9% of scored vulnerabilities.

Timeline

1. 20-10-2025
   PublishedVulnerability first disclosed.
2. 11-05-2026
   Last modifiedVulnerability information updated.

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.

No weakness data has been published for this record.