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CVE-2026-27124

CVE-2026-27124 · FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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 8.2 · High · EPSS 0.3% · Fix available

Published
Updated

Stack: python

Affected products and versions

  • fastmcp

    Versions
    • < 3.2.0: Affected

    No fix published

  • fastmcp PyPI

    Versions
    • 0.1.0
    • 0.2.0
    • 0.3.0
    • 0.3.1
    • 0.3.2
    • 0.3.3
    • 0.3.4
    • 0.3.5
    • 0.4.0
    • 0.4.1
    • 1.0
    • 2.0.0
    • 2.1.0
    • 2.1.1
    • 2.1.2
    • 2.10.0
    • 2.10.1
    • 2.10.2
    • 2.10.3
    • 2.10.4
    • 2.10.5
    • 2.10.6
    • 2.11.0
    • 2.11.1
    • 2.11.2
    • 2.11.3
    • 2.12.0
    • 2.12.0rc1
    • 2.12.1
    • 2.12.2
    • 2.12.3
    • 2.12.4
    • 2.12.5
    • 2.13.0
    • 2.13.0.1
    • 2.13.0.2
    • 2.13.0rc1
    • 2.13.0rc2
    • 2.13.0rc3
    • 2.13.1
    • 2.13.2
    • 2.13.3
    • 2.14.0
    • 2.14.1
    • 2.14.2
    • 2.14.3
    • 2.14.4
    • 2.14.5
    • 2.14.6
    • 2.14.7
    • 2.2.0
    • 2.2.1
    • 2.2.10
    • 2.2.2
    • 2.2.3
    • 2.2.4
    • 2.2.5
    • 2.2.6
    • 2.2.7
    • 2.2.8
    • 2.2.9
    • 2.3.0
    • 2.3.0rc1
    • 2.3.1
    • 2.3.2
    • 2.3.3
    • 2.3.4
    • 2.3.5
    • 2.4.0
    • 2.5.0
    • 2.5.1
    • 2.5.2
    • 2.6.0
    • 2.6.1
    • 2.7.0
    • 2.7.1
    • 2.8.0
    • 2.8.1
    • 2.9.0
    • 2.9.1
    • 2.9.2
    • 3.0.0
    • 3.0.0b1
    • 3.0.0b2
    • 3.0.0rc1
    • 3.0.0rc2
    • 3.0.0rc3
    • 3.0.1
    • 3.0.2
    • 3.1.0
    • 3.1.1
    Affected ranges
    • ECOSYSTEM: < 3.2.0

    Update to 3.2.0

Original sources

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