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


- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** GHSA-fmvx-487g-mrww

## 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 (Missing Authentication for Critical Functionality)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-61542 and fix it if it is affected.

What it is: CVE-2026-61542 is a high-severity vulnerability in drhelius Gearboy, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-61542 in the wild and no public exploit code.

Affected product: drhelius Gearboy. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-61542/ (Markdown: https://insights.sbomify.com/CVE-2026-61542/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-61542
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-61542
- OSV: https://osv.dev/vulnerability/CVE-2026-61542

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-61542/
Summaries are generated and may contain mistakes; the official description above is the record.