---
id: CVE-2026-61542
title: >-
  Gearboy advisory / Gearsystem body: Unauthenticated network exposure of MCP
  HTTP tools
summary: >-
  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 reachab…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L'
cvssSource: cna
cwe:
  - CWE-306
vendor: drhelius
product: Gearboy
affected:
  - Gearboy < 3.8.7
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-11-03T14:02:27.302687Z'
exploitAvailable: true
published: '2026-10-28'
updated: '2026-11-03'
sourceUpdated: '2026-11-03T14:11:09.339Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-61542'
references:
  - url: >-
      https://github.com/drhelius/Gearboy/security/advisories/GHSA-fmvx-487g-mrww
    label: >-
      https://github.com/drhelius/Gearboy/security/advisories/GHSA-fmvx-487g-mrww
  - url: >-
      https://github.com/drhelius/Gearboy/commit/e2ead98e2fac41e9df5a499e9e421c6a0e73f1bc
    label: >-
      https://github.com/drhelius/Gearboy/commit/e2ead98e2fac41e9df5a499e9e421c6a0e73f1bc
  - url: 'https://github.com/drhelius/Gearboy/releases/tag/3.8.7'
    label: 'https://github.com/drhelius/Gearboy/releases/tag/3.8.7'
tags:
  - cve.org
  - exploit-available
epss: 0.00307
epssPercentile: 0.23601
ingestedAt: '2026-10-29T15:37:07.561Z'
---

## Overview

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.

## Affected

- `Gearboy < 3.8.7`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.