# GHSA-rcfx-77hg-w2wv: FastMCP updated to MCP 1.23+ due to CVE-2025-66416

> FastMCP allowed vulnerable MCP SDK versions, requiring an upgrade to mitigate risks from CVE-2025-66416.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not stated
- **Attackable:** Not stated
- **Victim action needed:** Not stated
- **Fix available:** Yes
- **Published:** 26 Dec 2025

## What is GHSA-rcfx-77hg-w2wv?

GHSA-rcfx-77hg-w2wv is a vulnerability in fastmcp, published on 26 Dec 2025. 

### Official description

There was a recent CVE report on MCP: https://nvd.nist.gov/vuln/detail/CVE-2025-66416. 

FastMCP does not use any of the affected components of the MCP SDK directly. However, FastMCP versions prior to 2.14.0 did allow MCP SDK versions <1.23 that were vulnerable to CVE-2025-66416. Users should upgrade to FastMCP 2.14.0 or later.

## Which versions are affected by GHSA-rcfx-77hg-w2wv?

2 open source packages ship an affected version, including fastmcp.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `fastmcp` | PyPI | All versions | 2.14.0 |
| `fastmcp` | PyPI | All versions | 2.14.0 |

## How do I fix GHSA-rcfx-77hg-w2wv?

Upgrade fastmcp to 2.14.0 or later.

## Is GHSA-rcfx-77hg-w2wv being exploited?

There is no known exploitation of GHSA-rcfx-77hg-w2wv in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-rcfx-77hg-w2wv and fix it if it is affected.

What it is: GHSA-rcfx-77hg-w2wv is a vulnerability in fastmcp, published on 26 Dec 2025. 
Exploitation: There is no known exploitation of GHSA-rcfx-77hg-w2wv in the wild and no public exploit code.

Affected packages and fixed versions:
- fastmcp (PyPI): affected all versions; fixed in 2.14.0
- fastmcp (PyPI): affected all versions; fixed in 2.14.0

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/GHSA-rcfx-77hg-w2wv/ (Markdown: https://insights.sbomify.com/GHSA-rcfx-77hg-w2wv/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-rcfx-77hg-w2wv

---
From sbomify Insights: https://insights.sbomify.com/GHSA-rcfx-77hg-w2wv/
Summaries are generated and may contain mistakes; the official description above is the record.