Vulnerability · Published Oct 28, 2026 · Assigned by GitHub_M

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

High 8.6

In plain English

A high-severity missing authentication in Gearboy from drhelius. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities).

Severity (CVSS 3.1)8.6High

Exploit odds (30 days)0.3%top 76.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected products (as reported)

Vendor	Product	Versions
drhelius	Gearboy	< 3.8.7

Weakness: CWE-306 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

References

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