FastMCP — Command Injection (CVE-2025-64340)
Date: 2026-04
Affected: jlowin/fastmcp
Attack vector: command-injection
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2025-64340
CWE: CWE-78
CVSS: 6.7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H)

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.


Mitigations:

Architectural layers (MAESTRO):