FastMCP versions 3.0.0–3.4.9 and 4.0.0–4.1.1 have an authorization 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 the server applies transforms to components but does not reauthorize the transformed component before returning it on direct lookups. Fixes are available in FastMCP 3.4.10 and 4.1.2.