Cross-Site Scripting (XSS) vulnerability exists in SourceCodester AI Font Matcher (nid=18425, 2025-10-10) that allows remote attackers to execute arbitrary JavaScript in victims' browsers. The vulnerability occurs in the webfonts API handling mechanism where font family names are not properly sanitized. An attacker can intercept fetch requests to the webfonts endpoint and inject malicious JavaScript payloads through font family names, resulting in session cookie theft, account hijacking, and unauthorized actions performed on behalf of authenticated users. The vulnerability can be exploited by injecting a fetch hook that returns controlled font data containing malicious scripts.