# CVE-2025-37879: 9p/net: fix improper handling of bogus negative read/write replies

> A signed integer comparison flaw in the Linux kernel 9p network client allows a malicious server to trigger a null pointer dereference, causing a denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 May 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-70153, BELL-CVE-2025-37879, DEBIAN-CVE-2025-37879, GHSA-9hq9-gv35-c42w, ROOT-OS-DEBIAN-11-CVE-2025-37879, ROOT-OS-DEBIAN-12-CVE-2025-37879, ROOT-OS-UBUNTU-2204-CVE-2025-37879, ROOT-OS-UBUNTU-2404-CVE-2025-37879, UBUNTU-CVE-2025-37879

## What is CVE-2025-37879?

CVE-2025-37879 is a critical vulnerability in Debian Debian Linux, published on 9 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

9p/net: fix improper handling of bogus negative read/write replies

In p9_client_write() and p9_client_read_once(), if the server
incorrectly replies with success but a negative write/read count then we
would consider written (negative) <= rsize (positive) because both
variables were signed.

Make variables unsigned to avoid this problem.

The reproducer linked below now fails with the following error instead
of a null pointer deref:
9pnet: bogus RWRITE count (4294967295 > 3)

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2025-37879?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-37879?

Apply the vendor's patch.

## Is CVE-2025-37879 being exploited?

There is no known exploitation of CVE-2025-37879 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [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-2025-37879 and fix it if it is affected.

What it is: CVE-2025-37879 is a critical vulnerability in Debian Debian Linux, published on 9 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-37879 in the wild and no public exploit code.

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-2025-37879/ (Markdown: https://insights.sbomify.com/CVE-2025-37879/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-37879
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-37879
- OSV: https://osv.dev/vulnerability/CVE-2025-37879

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-37879/
Summaries are generated and may contain mistakes; the official description above is the record.