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fastmcp vulnerabilities

Vulnerabilities published for fastmcp in the last 30 days: 2. Listed in the KEV catalogue: 0.

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Vulnerabilities: 10

  1. GHSA-7xgj-8392-5q4r

    Medium · CVSS 6.8Fix available

    FastMCP: Post-transform component authorization is skipped on direct calls

    ## Maintainer assessment and remediation This report is accepted as a FastMCP authorization vulnerability. In supported configurations, a server transform can change the metadata used by a component's authorization policy. Direct lookups previously checked the original component but returned the transformed component without rechecking its policy. A client that knows the component identifier can invoke a tool or retrieve a resource or prompt that the configured policy denies. The fixes authorize the final transformed tools, resources, templates, and prompts. A denied concrete resource also shadows a matching resource template at its URI, pr

    fastmcp fastmcpPython
    • Update to 3.4.10
    • Update to 4.1.2
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  2. GHSA-vqqp-x5qm-5qp4

    Medium · CVSS 5.9Fix available

    FastMCP MCP client wrappers construct M2M OAuth providers without issuer binding — client secret redirectable to attacker-advertised authorization server

    ## Maintainer assessment and remediation This report is accepted as a FastMCP credential-binding vulnerability. Affected versions of the OAuth client credentials providers do not expose the authorization-server issuer that owns pre-registered credentials. An untrusted or compromised MCP server can therefore advertise a different authorization server and receive the client secret or a signed assertion. Signing keys themselves remain local; assertion replayability depends on the assertion source and audience policy. Affected stable versions are 4.0.0–4.1.1 of `fastmcp` and `fastmcp-slim`. The wrappers were introduced in 4.0.0a1; 3.x does not

    fastmcpPython
    • Update to 4.1.2
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  3. CVE-2026-27124

    High · CVSS 8.2EPSS 0.3%Fix available

    FastMCP: Missing Consent Verification in OAuth Proxy Callback Facilitates Confused Deputy Vulnerabilities

    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.

    fastmcpPython
    • Update to 3.2.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗

  4. CVE-2025-64340

    Medium · CVSS 6.7EPSS 0.73%Fix available

    FastMCP has a Command Injection vulnerability - Gemini CLI

    FastMCP is the standard framework for building MCP applications. Prior to version 3.2.0, server names containing shell metacharacters (e.g., &) can cause command injection on Windows when passed to fastmcp install claude-code or fastmcp install gemini-cli. These install paths use subprocess.run() with a list argument, but on Windows the target CLIs often resolve to .cmd wrappers that are executed through cmd.exe, which interprets metacharacters in the flattened command string. This issue has been patched in version 3.2.0.

    fastmcpPython
    • Update to 3.2.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  5. CVE-2026-32871

    Critical · CVSS 10EPSS 1.37%Fix available

    FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability

    FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. The RequestDirector class is responsible for constructing HTTP requests to the backend service. A vulnerability exists in the _build_url() method. When an OpenAPI operation defines path parameters (e.g., /api/v1/users/{user_id}), the system directly substitutes parameter values into the URL template string without URL-encoding. Subsequently, urllib.parse.urljoin() resolves the final URL. Since urljoin() interprets ../ sequences as directory traversal, an atta

    fastmcpPython
    • Update to 3.2.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  6. CVE-2025-69196

    High · CVSS 7.4EPSS 0.37%Fix available

    FastMCP OAuth Proxy token reuse across MCP servers

    FastMCP is the standard framework for building MCP applications. Prior to version 2.14.2, the server does not properly respect the resource parameter submitted by the client in the authorization and token request. Instead of issuing the token explicitly for the MCP server, the token is issued for the base_url passed to the OAuthProxy during initialization. This issue has been patched 2.14.2.

    fastmcpPython
    • Update to 2.14.2
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  7. GHSA-rcfx-77hg-w2wv

    Not ratedFix available

    FastMCP updated to MCP 1.23+ due to CVE-2025-66416

    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.

    fastmcpPython
    • Update to 2.14.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  8. GHSA-c2jp-c369-7pvx

    Not ratedFix available

    FastMCP Auth Integration Allows for Confused Deputy Account Takeover

    ### Summary FastMCP documentation [covers the scenario](https://gofastmcp.com/integrations/azure) where it is possible to use Entra ID or other providers for authentication. In this context, because Entra ID does not support Dynamic Client Registration (DCR), the FastMCP-hosted MCP server is acting as the authorization provider, as declared in the Protected Resource Metadata (PRM) document hosted on the server. For example, on a local MCP server, it may be hosted here: ```http http://localhost:8000/.well-known/oauth-protected-resource ``` And the JSON representation of the PRM document: ```json { "resource": "http://localhost:8000/mcp"

    fastmcpPython
    • Update to 2.13.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗Source advisory 3 ↗

  9. CVE-2025-62801

    Medium · CVSS 5.4EPSS 0.23%Fix available

    FastMCP vulnerable to windows command injection in FastMCP Cursor installer via server_name

    FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0, a command-injection vulnerability lets any attacker who can influence the server_name field of an MCP execute arbitrary OS commands on Windows hosts that run fastmcp install cursor. This vulnerability is fixed in 2.13.0.

    fastmcpPython
    • Update to 2.13.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗

  10. CVE-2025-62800

    Medium · CVSS 5.3EPSS 0.28%Fix available

    FastMCP vulnerable to reflected XSS in client's callback page

    FastMCP is the standard framework for building MCP applications. Versions prior to 2.13.0 have a reflected cross-site scripting vulnerability in the OAuth client callback page (oauth_callback.py) where unescaped user-controlled values are inserted into the generated HTML, allowing arbitrary JavaScript execution in the callback server origin. The issue is fixed in version 2.13.0.

    fastmcpPython
    • Update to 2.13.0
    Published Updated
    Source advisory 1 ↗Source advisory 2 ↗

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