FastMCP versions 3.0.0 through 4.1.1 have an authorization bypass vulnerability where direct calls to transformed components skip the final authorization check. This allows low-privilege users to invoke protected tools, resources, templates, or prompts that should be denied. The issue arises because transforms are applied before authorization, but the authorization check is not re-applied to the transformed component. Fixes are available in FastMCP 3.4.10 and 4.1.2.