CVE-2026-21873 Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`

NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.subpages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been...

CVE-2026-21873

NiceGUI (Python UI framework) has a cross-site scripting risk in versions 2.22.0–3.4.1 due to an unsafe pushstate listener in ui.sub_pages that lets an attacker manipulate the URL fragment via an iframe. The issue is exploitable without user interaction and affects pages embeddable in iframes. A ...