Command Injection Affecting fastmcp package, versions [,2.13.0rc1)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-FASTMCP-13745516
- published30 Oct 2025
- disclosed28 Oct 2025
- creditNil Ash
Introduced: 28 Oct 2025
NewCVE-2025-62801 (opens in a new tab)How to fix?
Upgrade fastmcp to version 2.13.0rc1 or higher.
Overview
fastmcp is a The fast, Pythonic way to build MCP servers and clients.
Affected versions of this package are vulnerable to Command Injection via the server_name field. An attacker can execute arbitrary OS commands by supplying crafted input to this field during the installation process on Windows hosts that run the install cursor functionality.
PoC
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()