AIKIDO-2026-10826
fastmcp is vulnerable to Confused Deputy
71
High Risk
This Affects:
fastmcpTL;DR
The OAuth proxy consent screen can silently reuse remembered approvals in configuration modes where that shortcut is enabled. Cross-site navigations into the authorize endpoint could previously hit that silent path without proving a same-client browsing context. The handler now treats Sec-Fetch-Site as a gate and drops to the interactive prompt when the navigation looks cross-site or the header is absent, so a third-party authorization server or crafted redirect cannot auto-approve on the user’s behalf. Approval cookies for future visits are only written when the remembered-consent mode is actually enabled.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range.
Background info
fastmcp is vulnerable to Confused Deputy in versions 3.2.0 - 3.2.4.
How to fix this
Upgrade the fastmcp library to the patch version.
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SOC 2Compliant
ISO 27001Compliant