# CVE-2025-37947: ksmbd: prevent out-of-bounds stream writes by validating *pos

> An out-of-bounds write in the ksmbd kernel module allows attackers to potentially execute code or escalate privileges via crafted stream write requests.

- **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:** 20 May 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-37947, DEBIAN-CVE-2025-37947, GHSA-c42x-xw5m-9j9p, ROOT-OS-DEBIAN-12-CVE-2025-37947, ROOT-OS-UBUNTU-2204-CVE-2025-37947, ROOT-OS-UBUNTU-2404-CVE-2025-37947, UBUNTU-CVE-2025-37947

## What is CVE-2025-37947?

CVE-2025-37947 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 20 May 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: prevent out-of-bounds stream writes by validating *pos

ksmbd_vfs_stream_write() did not validate whether the write offset
(*pos) was within the bounds of the existing stream data length (v_len).
If *pos was greater than or equal to v_len, this could lead to an
out-of-bounds memory write.

This patch adds a check to ensure *pos is less than v_len before
proceeding. If the condition fails, -EINVAL is returned.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2025-37947?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37947?

Apply the vendor's patch.

## Is CVE-2025-37947 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-37947 exists.

Public exploit code:

- Blog Post: https://blog.doyensec.com/2025/10/08/ksmbd-3.html (github_poc): https://github.com/doyensec/KSMBD-CVE-2025-37947

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- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-37947 and fix it if it is affected.

What it is: CVE-2025-37947 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 20 May 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-37947 exists.

Affected product: Debian Debian Linux. 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-2025-37947/ (Markdown: https://insights.sbomify.com/CVE-2025-37947/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37947
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37947
- OSV: https://osv.dev/vulnerability/CVE-2025-37947

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37947/
Summaries are generated and may contain mistakes; the official description above is the record.