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

CVE ID : CVE-2026-21873

Published : Jan. 8, 2026, 9:50 a.m. | 37 minutes ago

Description : 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.sub_pages 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 patched in version 3.5.0.

Severity: 0.0 | NA

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