# CVE-2025-40039: ksmbd: Fix race condition in RPC handle list access

CVE-2025-40039 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-40039, released October 28, 2025. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2025-40039
- Priority: Routine
- CVSS: 4.7 (Moderate)
- EPSS: 0.0031
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 28, 2025
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-40039

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.162-1 | [DEBIAN-CVE-2025-40039](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40039.md) | Oct 28, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.12.57-1 | [DEBIAN-CVE-2025-40039](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40039.md) | Oct 28, 2025 |
| Linux | linux Debian 14 | 6.17.6-1 | [DEBIAN-CVE-2025-40039](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40039.md) | Oct 28, 2025 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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