GHSA-7xgj-8392-5q4r: FastMCP: Post-transform component authorization is skipped on direct calls
FastMCP’s direct component paths can return a transformed component before its applicable AuthCheck, allowing low-privilege callers to execute hidden protected behavior. I reproduced this against FastMCP 4.1.0 and commit e2fcc412001ff7414095c5dc282f94c70299a612 using only an in-process FastMCP server. The attacker does not have server-side access and does not control FastMCP configuration.
References
- github.com/PrefectHQ/fastmcp/commit/85df42fbf2aa631cc81e0f986718b314128e91df
- github.com/PrefectHQ/fastmcp/commit/8649ba5fc91a68568a69729497edeb804a064332
- github.com/PrefectHQ/fastmcp/pull/5933
- github.com/PrefectHQ/fastmcp/pull/5934
- github.com/PrefectHQ/fastmcp/releases/tag/v3.4.10
- github.com/PrefectHQ/fastmcp/releases/tag/v4.1.2
- github.com/PrefectHQ/fastmcp/security/advisories/GHSA-7xgj-8392-5q4r
- github.com/advisories/GHSA-7xgj-8392-5q4r
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