---
id: "CVE-2026-121969"
kind: "vulnerability"
aliases: ["CVE-2026-121969"]
title: "netrek-client-cow: stack overflow in message handling lets a server crash the client"
severity: "high"
cvss: 7.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["c", "netrek", "netrek-client-cow", "package"]
not_affected_if: ["client-not-installed", "trusted-network-only"]
published_at: "2026-11-04T21:18:06+00:00"
first_seen_at: "2026-11-04T21:49:18+00:00"
updated_at: "2026-11-04T21:50:59+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121969", "first_seen_at": "2026-11-04T21:49:18+00:00"}]
exploit_sources: []
---

# netrek-client-cow: stack overflow in message handling lets a server crash the client

netrek-client-cow through 3.3.3 has a stack buffer overflow in handleSMessage() in short.c. A malicious Netrek server or an attacker on the plaintext connection can send oversized message packets that write server-controlled bytes onto the stack, crashing the client.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed netrek-client-cow version against the sources; versions through `3.3.3` are affected.
- Look for the `handleSMessage()` function in `short.c` in your build if you compile from source.

## Fix

- Patch linked in the sources (github.com); the fixed version is not stated in the sources.

## Timeline

- 2026-11-04T21:49:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121969

## Documents

- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/netrek-client-cow-through-3.3.3-stack-buffer-overflow-via-handlesmessage
- [fix] Patch: github.com https://github.com/quozl/netrek-client-cow/commit/fb322e74abee3b0b76a9c5a31df6aab5585d3127

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_