XSS in Zauberzeug Nicegui
CVE-2026-21871
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000
Affected products
- Zauberzeug Nicegui — versions >= 2.13.0, < 3.5.0
Weakness classification (CWE)
References
- github.com/zauberzeug/nicegui/security/advisories/GHSA-7grm-h62g-5m97 (Exploit, Vendor Advisory)
- github.com/zauberzeug/nicegui/releases/tag/v3.5.0 (Release Notes)
Frequently asked questions
- What is CVE-2026-21871?
- CVE-2026-21871 is a medium-severity vulnerability in Zauberzeug Nicegui, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-01-08.
- How severe is CVE-2026-21871?
- Medium severity. CVSS v3 base score is 6.1 out of 10.