Command Injection Affecting fastmcp package, versions [,3.2.0)
Threat Intelligence
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-15871029
- published1 Apr 2026
- disclosed31 Mar 2026
- creditNil Ash
Introduced: 31 Mar 2026
NewCVE-2025-64340 (opens in a new tab)How to fix?
Upgrade fastmcp to version 3.2.0 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 subprocess-backed install commands. An attacker can execute arbitrary commands with the privileges of the user running the process by supplying a server name containing shell metacharacters, which are interpreted by the Windows command shell when invoking certain CLI wrappers.
Note:
This is only exploitable if the target CLI is installed as a .cmd wrapper on a Windows host.
PoC
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)]