Description
NiceGUI is a Python-based UI framework. Versions 3.3.1 and below are vulnerable to Reflected XSS through its ui.add_css, ui.add_scss, and ui.add_sass functions. The functions lack proper sanitization or encoding for the JavaScript context they generate. An attacker can break out of the intended <style> or <script> tags by injecting closing tags (e.g., </style> or </script>), allowing for the execution of arbitrary JavaScript. This issue is fixed in version 3.4.0.
Affected products
zauberzeug: nicegui
References3
- github.com/zauberzeug/nicegui/security/advisories/GHSA-72qc-wxc… ExploitVendor Advisory
- github.com/zauberzeug/nicegui/security/advisories/GHSA-72qc-wxc… ExploitVendor Advisory
- github.com/zauberzeug/nicegui/commit/a8fd25b7d5e23afb1952d0f60a… Patch
Metrics
- CVSS 3.1
-
6.1
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - EPSS — exploit probability
- 0% percentile: 22 · as of 11 November 2026
- CWE
- CWE-79
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.