How severe is GHSA-rcfx-77hg-w2wv?

No CVSS score has been assigned to GHSA-rcfx-77hg-w2wv yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-rcfx-77hg-w2wv?

GHSA-rcfx-77hg-w2wv affects the following packages: fastmcp (PyPI). Ecosystems affected: PyPI.

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

Update fastmcp to 2.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rcfx-77hg-w2wv is resolved across your whole dependency graph.

How do I detect GHSA-rcfx-77hg-w2wv in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastmcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-rcfx-77hg-w2wv if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-rcfx-77hg-w2wv actively exploited in the wild?

No public exploit code has been indexed for GHSA-rcfx-77hg-w2wv yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-rcfx-77hg-w2wv published, and has it been updated?

GHSA-rcfx-77hg-w2wv was published on December 26, 2025 and was last updated on December 26, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

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

GHSA-rcfx-77hg-w2wv is a security vulnerability in fastmcp. A fix is available for fastmcp — see the affected versions and patch details below.

Published

Dec 26, 2025

Updated

Dec 26, 2025

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Dec 26, 2025 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

🐍fastmcp

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`fastmcp`	all versions	2.14.0`pip install --upgrade 'fastmcp==2.14.0'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastmcp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update fastmcp to 2.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rcfx-77hg-w2wv is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

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