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Vulnerability record · CVE-2026-21873 · published 8 January 2026

CVE-2026-21873: Zauberzeug nicegui cross-site scripting vulnerability

Zauberzeug · Nicegui

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.

6.1 CVSS 3.1 Medium EPSS 0.26% · top 83.6% CWE-79 · Cross-site scripting
6.1CVSS 3.1 base score
0.26%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 2.22.0 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.

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-mhpg-c27v-6mxr ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-21873), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.