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

> A race condition in the Linux kernel's ksmbd module allows attackers to cause data corruption or use-after-free, potentially leading to code execution or system crashes.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Oct 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-78383, BELL-CVE-2025-40039, DEBIAN-CVE-2025-40039, GHSA-258w-3pq9-4jh3, ROOT-OS-DEBIAN-12-CVE-2025-40039, ROOT-OS-DEBIAN-13-CVE-2025-40039, ROOT-OS-UBUNTU-2204-CVE-2025-40039, ROOT-OS-UBUNTU-2404-CVE-2025-40039, UBUNTU-CVE-2025-40039

## What is CVE-2025-40039?

CVE-2025-40039 is a high-severity vulnerability in Linux kernel, published on 28 Oct 2025. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-40039?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-40039?

Apply the vendor's patch.

## Is CVE-2025-40039 being exploited?

There is no known exploitation of CVE-2025-40039 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40039 and fix it if it is affected.

What it is: CVE-2025-40039 is a high-severity vulnerability in Linux kernel, published on 28 Oct 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40039 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40039/ (Markdown: https://insights.sbomify.com/CVE-2025-40039/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40039
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40039
- OSV: https://osv.dev/vulnerability/CVE-2025-40039

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40039/
Summaries are generated and may contain mistakes; the official description above is the record.