CVE-2026-32871
CriticalCVSS 10.0Exploitation Probability (EPSS)
Elevated risk59th percentile - higher than 59% of all known CVEs
Summary
In FastMCP prior to version 3.2.0, the _build_url() method in the RequestDirector class lacks URL encoding of path parameters. This allows an attacker to inject ../ sequences and perform a path traversal attack, enabling access to arbitrary internal endpoints.
Risk Assessment
An attacker can bypass the intended API prefix and access internal services, leading to authenticated SSRF. This may result in unauthorized access to sensitive data or internal systems.
Recommendation
Immediately upgrade FastMCP to version 3.2.0 or later, which contains the fix for this vulnerability.
Other vulnerabilities in FastMCP
See all- CVE-2026-27124Medium
In FastMCP prior to version 3.2.0, a Confused Deputy vulnerability was found in the OAuthProxy component. During GitHub OAuth integration, the server does not properly validate user consent, which combined with GitHub skipping the consent screen enables an attack.
- CVE-2025-64340Medium
A vulnerability in FastMCP before version 3.2.0. Server names containing shell metacharacters (e.g., &) can cause command injection on Windows during installation via fastmcp install claude-code or gemini-cli.
- CVE-2025-69196Medium
In the FastMCP library before version 2.14.2, the server does not properly respect the resource parameter submitted by the client in the authorization and token request. The token is issued for the base_url passed to the OAuthProxy during initialization, not for the specific MCP server.
- CVE-2025-62801High
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.
- CVE-2025-62800Medium
FastMCP 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.
Original NVD description (English source)
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 attacker controlling a path parameter can perform path traversal attacks to escape the intended API prefix and access arbitrary backend endpoints. This results in authenticated SSRF, as requests are sent with the authorization headers configured in the MCP provider. This issue has been patched in version 3.2.0.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS