Gearboy advisory / Gearsystem body: Unauthenticated network exposure of MCP HTTP tools

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-61542
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-28 20:18:27 UTC
Updated2026-10-28 20:18:27 UTC
DescriptionGearboy 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.

Risk And Classification

Primary CVSS: v3.1 8.6 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

Problem Types: CWE-306 | CWE-306 CWE-306: Missing Authentication for Critical Function

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.6HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
3.1CNADECLARED8.6HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Drhelius Gearboy affected < 3.8.7 Not specified

References

ReferenceSourceLinkTags
github.com/drhelius/Gearboy/commit/e2ead98e2fac41e9df5a499e9e421c6a0e73f1bc [email protected] github.com
github.com/drhelius/Gearboy/security/advisories/GHSA-fmvx-487g-mrww [email protected] github.com
github.com/drhelius/Gearboy/releases/tag/3.8.7 [email protected] github.com
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