CVE-2025-66469

NiceGUI is a Python-based UI framework. Versions 3.3.1 and below are vulnerable to Reflected XSS through its ui.add_css, ui.add_scss, and ui.add_sass functions. The functions lack proper sanitization or encoding for the JavaScript context they generate. An attacker can break out of the intended or <script> tags by injecting closing tags (e.g., or ), allowing for the execution of arbitrary JavaScript. This issue is fixed in version 3.4.0.