CVE-2026-61542 Gearboy advisory / Gearsystem body: Unauthenticated network exposure of MCP HTTP tools
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-61542?
CVE-2026-61542 is a high-severity vulnerability in drhelius Gearboy, published on 28 Oct 2026.
Official 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.
Weakness: CWE-306
Which versions are affected by CVE-2026-61542?
How do I fix CVE-2026-61542?
No fix has been published for CVE-2026-61542 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-61542 being exploited?
There is no known exploitation of CVE-2026-61542 in the wild and no public exploit code.
Sources
Also known as GHSA-fmvx-487g-mrww.