CVE-2025-40039: Linux Kernel

Medium severity, CVSS 4.7. EPSS: 0.3% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: ksmbd: Fix race condition in RPC handle list access The 'sess->rpc_handle_list' XArray manages RPC handles within a ksmbd session. Access to this list is intended to be protected by 'sess->rpc_lock' (an rw_semaphore). However, the locking implementation was flawed, leading to potential race conditions. In ksmbd_session_rpc_open(), the code incorrectly acquired only a read lock before calling xa_store() and xa_erase(). Since these operations modify the XArray structure, a write lock is required to ensure exclusive access and prevent data corruption from concurrent modifications. Furthermore, ksmbd_session_rpc_method() accessed the list using xa_load() without holding any lock at all. This could lead to reading inconsistent data or a potential use-after-free if an entry is concurrently removed and the pointer is dereferenced. Fix these issues by: 1. Using down_write() and up_write() in ksmbd_session_rpc_open() to ensure exclusive access during XArray modification, and ensuring the lock is correctly released on error paths. 2. Adding down_read() and up_read() in ksmbd_session_rpc_method() to safely protect the lookup.

Affected products

• Linux Linux Kernel: from 5.15.145, before 5.16 (fixed in 5.16); from 6.1.71, before 6.2 (fixed in 6.2); from 6.3, before 6.6.123 (fixed in 6.6.123); from 6.7, before 6.12.53 (fixed in 6.12.53); from 6.13, before 6.17.3 (fixed in 6.17.3)

Published 2025-10-28. Last modified 2026-07-30.