A stored Cross-Site Scripting (XSS) vulnerability exists in the mintplex-labs/anything-llm application, affecting versions up to and including the latest before 1.0.0. The vulnerability arises from the application's failure to properly sanitize and validate user-supplied URLs before embedding them into the application UI as external links with custom icons. Specifically, the application does not prevent the inclusion of 'javascript:' protocol payloads in URLs, which can be exploited by a user with manager role to execute arbitrary JavaScript code in the context of another user's session.

This flaw can be leveraged to steal the admin's authorization token by crafting malicious URLs that, when clicked by the admin, send the token to an attacker-controlled server. The attacker can then use this token to perform unauthorized actions, escalate privileges to admin, or directly take over the admin account. The vulnerability is triggered when the malicious link is opened in a new tab using either the CTRL + left mouse button click or the mouse scroll wheel click, or in some non-updated versions of modern browsers, by directly clicking on the link.