Intel

AIKIDO-2026-10825

fastmcp is vulnerable to Open Redirect

Open Redirect Pre-CVE
Found by Aikido Intel before public disclosure or CVE publication.
Published May 19, 2026

80

High Risk

This Affects:

PYTHONfastmcp
3.0.0 - 3.2.4
Fixed in 3.3.0
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TL;DR

Redirect URI allowlisting matched paths with fnmatch semantics where wildcards can span slash boundaries. An attacker could register a redirect URI whose path contains dot-segments such that it matches an operator prefix during validation yet normalizes to a different path when the browser resolves a redirect target. The validator now rejects any path containing . or .. segments in both raw and percent-decoded forms before pattern matching, closing prefix bypasses that relied on RFC 3986 dot-segment removal.

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 Open Redirect in versions 3.0.0 - 3.2.4.

How to fix this

Upgrade the fastmcp library to the patch version.