A vulnerability was discovered in the `fast-agent serve` command. By default, it binds to all network interfaces on port 8000 without authentication, allowing any host with network access to control the agent. When the `--shell` flag is used, an unauthenticated remote client can execute arbitrary OS commands, resulting in unauthenticated remote code execution (RCE). This is due to the agent's default configuration in `cli/commands/serve.py`, `mcp/server/agentserver.py`, and `tools/localshellexecutor.py`. This vulnerability affects versions up to 0.7.20, including the Docker Python 3.13-slim image.