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Vulnerability record · CVE-2026-21871 · published 8 January 2026

CVE-2026-21871: Zauberzeug nicegui cross-site scripting vulnerability

Zauberzeug · Nicegui

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.

6.1 CVSS 3.1 Medium EPSS 0.28% · top 81.9% CWE-79 · Cross-site scripting
6.1CVSS 3.1 base score
0.28%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References, 1 tagged exploit
17 Jun 2026Last modified by NVD

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0 Release Notes
https://github.com/zauberzeug/nicegui/security/advisories/GHSA-7grm-h62g-5m97 ExploitVendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2026-21871), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.