HackerOne Disclosed Reports - 2025-09-30

Medium
resolved

`use-mcp`'s oauth2 process uses a window.open call with untrusted mcp server provided data allowing for code execution under the page using it

Bug reported by Raymond was disclosed at September 30, 2025, 8:15 am   |   Cross-site Scripting (XSS) - Generic

The `authorizeEndpoint` parameter from `use-mcp` version was susceptible to XSS. Sanitization of that parameter was added in version 0.0.10 of use-mcp. A skilled attacker was able to turn this XSS into code execution on the client.