XSS in Zauberzeug Nicegui
CVE-2026-21873
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (16.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 16.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.000
Affected products
- Zauberzeug Nicegui — versions >= 2.22.0, < 3.5.0
Weakness classification (CWE)
References
- github.com/zauberzeug/nicegui/security/advisories/GHSA-mhpg-c27v-6mxr (Exploit, Vendor Advisory)
- github.com/zauberzeug/nicegui/releases/tag/v3.5.0 (Release Notes)
Frequently asked questions
- What is CVE-2026-21873?
- CVE-2026-21873 is a high-severity vulnerability in Zauberzeug Nicegui, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-01-08.
- How severe is CVE-2026-21873?
- High severity. CVSS v3 base score is 7.2 out of 10.