CVE-2025-66469 NiceGUI Reflected XSS in ui.add_css, ui.add_scss, and ui.add_sass via Style Injection
Attackers can execute arbitrary JavaScript via reflected XSS in NiceGUI's CSS/SCSS/SASS injection functions due to lack of sanitization.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2025-66469?
CVE-2025-66469 is a medium-severity cross-site scripting vulnerability in zauberzeug nicegui, published on 8 Dec 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-79
Which versions are affected by CVE-2025-66469?
3 open source packages ship an affected version, including nicegui. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nicegui PyPI | All versions | 3.4.0 |
nicegui PyPI | All versions | 3.4.0 |
nicegui PyPI | All versions | 3.4.0 |
Products include Zauberzeug Nicegui.
How do I fix CVE-2025-66469?
Upgrade nicegui to 3.4.0 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2025-66469 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-66469 exists.
Other vulnerabilities in zauberzeug nicegui
- CVE-2026-25732 NiceGUI's Path Traversal via Unsanitized FileUpload.name Enables Arbitrary File Write
- CVE-2025-66645 NiceGUI Path Traversal Vulnerability in app.add_media_files() Allows Arbitrary File Reading
- CVE-2026-21873 Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`
- CVE-2026-33332 NiceGUI's unvalidated chunk size parameter in media routes can cause memory exhaustion
- CVE-2026-27156 NiceGUI has XSS via Code Injection
Sources
Also known as GHSA-72qc-wxch-74mg, PYSEC-2026-1697.