# CVE-2026-121969: netrek-client-cow through 3.3.3 Stack Buffer Overflow via handleSMessage


- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 4 Nov 2026
- **Updated:** 5 Nov 2026
- **Also known as:** GHSA-2v39-q9qf-3m9g, UBUNTU-CVE-2026-121969

## What is CVE-2026-121969?

CVE-2026-121969 is a high-severity vulnerability in quozl netrek-client-cow, published on 4 Nov 2026. 

### Official description

netrek-client-cow through 3.3.3 contains a stack-based buffer overflow vulnerability in handleSMessage() in short.c that allows malicious servers to overflow a 100-byte stack buffer by sending oversized SP_S_MESSAGE packets. A malicious Netrek server or man-in-the-middle on the plaintext TCP connection can send overlong or unterminated message bodies to write server-controlled bytes onto the stack and crash the client.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-121969?


## How do I fix CVE-2026-121969?

No fix has been published for CVE-2026-121969 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-121969 being exploited?

There is no known exploitation of CVE-2026-121969 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-121969 and fix it if it is affected.

What it is: CVE-2026-121969 is a high-severity vulnerability in quozl netrek-client-cow, published on 4 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-121969 in the wild and no public exploit code.

Affected product: quozl netrek-client-cow. 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-2026-121969/ (Markdown: https://insights.sbomify.com/CVE-2026-121969/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-121969
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121969
- OSV: https://osv.dev/vulnerability/CVE-2026-121969

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-121969/
Summaries are generated and may contain mistakes; the official description above is the record.