fastmcp / fastmcp-slim 3.0.0 through 3.4.9 and 4.0.0 through 4.1.1: FastMCP.get_tool(), get_resource(), get_resource_template() and get_prompt() (fastmcp/server/server.py) check a component's auth only before session transforms run and return the transformed component without re-checking, so a transform that changes what auth sees (for example adding an admin tag) is not enforced on direct calls and reads, letting an authenticated client invoke tools, read resources or render prompts it is not authorized for. Fixed in 3.4.10 and 4.1.2.