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CVE-2025-64340 — FastMCP has a Command Injection vulnerability - Gemini CLI

2026-10-02T09:42:51.743558+00:00

Affected: jlowin fastmcp

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.

GHSA-m8x7-r2rg-vh5g — FastMCP has a Command Injection vulnerability - Gemini CLI

2026-10-02T09:42:51.743689+00:00

Affected: PyPI: fastmcp

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.

PoC: ```python 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)] ```

``` fastmcp install claude-code server.py # or: fastmcp install gemini-cli server.py ```

On Windows, this opens Calculator via the `&calc` in the server name.

Impact: Arbitrary command execution with the privileges of the user running `fastmcp install`. Affects Windows hosts where the target CLI (one of claude, gemini) is installed as a `.cmd` wrapper. Does not affect macOS/Linux, and does not affect config-file-based install targets (cursor, goose, mcp-json).

Patched in #3522 by validating server names to reject shell metacharacters.

PYSEC-2026-2475 — FastMCP has a Command Injection vulnerability - Gemini CLI