Vulnerability Description
NiceGUI is a Python-based UI framework. From versions 2.13.0 to 3.4.1, there is a XSS risk in NiceGUI when developers pass attacker-controlled strings into ui.navigate.history.push() or ui.navigate.history.replace(). These helpers are documented as History API wrappers for updating the browser URL without page reload. However, if the URL argument is embedded into generated JavaScript without proper escaping, a crafted payload can break out of the intended string context and execute arbitrary JavaScript in the victim’s browser. Applications that do not pass untrusted input into ui.navigate.history.push/replace are not affected. This issue has been patched in version 3.5.0.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Zauberzeug | Nicegui | >= 2.13.0, < 3.5.0 |
Related Weaknesses (CWE)
References
- https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0Release Notes
- https://github.com/zauberzeug/nicegui/security/advisories/GHSA-7grm-h62g-5m97ExploitVendor Advisory
FAQ
What is CVE-2026-21871?
CVE-2026-21871 is a vulnerability with a CVSS score of 6.1 (MEDIUM). NiceGUI is a Python-based UI framework. From versions 2.13.0 to 3.4.1, there is a XSS risk in NiceGUI when developers pass attacker-controlled strings into ui.navigate.history.push() or ui.navigate.hi...
How severe is CVE-2026-21871?
CVE-2026-21871 has been rated MEDIUM with a CVSS base score of 6.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-21871?
Check the references section above for vendor advisories and patch information. Affected products include: Zauberzeug Nicegui.