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.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.

Affected

zauberzeug · nicegui

CVSS v3.1 NVD

6.1 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS v3.1 GITHUB

7.2 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

EPSS

0.26% chance of exploitation in the next 30 days, 17th percentile

Published

2026-01-08

Proof-of-concept exploits (1)

• advisories/GHSA-mhpg-c27v-6mxr

Security advisories

• zauberzeug/nicegui/security/advisories/GHSA-mhpg-c27v-6mxr
• zauberzeug/nicegui/releases/tag/v3.5.0

References

• CVE Record
• NVD entry