Vulnerability Description
FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, while testing the GitHubProvider OAuth integration, which allows authentication to a FastMCP MCP server via a FastMCP OAuthProxy using GitHub OAuth, it was discovered that the FastMCP OAuthProxy does not properly validate the user's consent upon receiving the authorization code from GitHub. In combination with GitHub’s behavior of skipping the consent page for previously authorized clients, this introduces a Confused Deputy vulnerability. This issue has been patched in version 3.2.0.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Jlowin | Fastmcp | < 3.2.0 |
Related Weaknesses (CWE)
References
- https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-rww4-4w9c-7733ExploitMitigationVendor Advisory
- https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-rww4-4w9c-7733ExploitMitigationVendor Advisory
FAQ
What is CVE-2026-27124?
CVE-2026-27124 is a vulnerability with a CVSS score of 6.1 (MEDIUM). FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, while testing the GitHubProvider OAuth integration, which allows authentication to a FastMCP MCP server via a F...
How severe is CVE-2026-27124?
CVE-2026-27124 has been rated MEDIUM with a CVSS base score of 6.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-27124?
Check the references section above for vendor advisories and patch information. Affected products include: Jlowin Fastmcp.