GHSA-rcfx-77hg-w2wv
FastMCP updated to MCP 1.23+ due to CVE-2025-66416
Blast Radius
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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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | fastmcp | all versions | 2.14.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for fastmcp. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether GHSA-rcfx-77hg-w2wv is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-rcfx-77hg-w2wv. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-rcfx-77hg-w2wv in your dependencies?
O3 detects GHSA-rcfx-77hg-w2wv across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.