CVE-2026-27124 | THREATINT

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.

PUBLISHED Reserved 2026-02-17 | Published 2026-04-03 | Updated 2026-04-03 | Assigner GitHub_M

HIGH: 8.2CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Problem types

CWE-441: Unintended Proxy or Intermediary ('Confused Deputy')

Product status

< 3.2.0

affected

References

github.com/...astmcp/security/advisories/GHSA-rww4-4w9c-7733 exploit

github.com/...astmcp/security/advisories/GHSA-rww4-4w9c-7733

cve.org (CVE-2026-27124)

nvd.nist.gov (CVE-2026-27124)

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