zauberzeug NiceGUI up to 3.6.x ui.html ui.markdown cross site scripting

Summaryinfo

A vulnerability has been found in zauberzeug NiceGUI up to 3.6.x and classified as problematic. Affected by this vulnerability is the function ui.markdown of the file ui.html. The manipulation leads to cross site scripting. This vulnerability is referenced as CVE-2026-25516. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in zauberzeug NiceGUI up to 3.6.x and classified as problematic. This issue affects the function ui.markdown of the file ui.html. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

NiceGUI is a Python-based UI framework. The ui.markdown() component uses the markdown2 library to convert markdown content to HTML, which is then rendered via innerHTML. By default, markdown2 allows raw HTML to pass through unchanged. This means that if an application renders user-controlled content through ui.markdown(), an attacker can inject malicious HTML containing JavaScript event handlers. Unlike other NiceGUI components that render HTML (ui.html(), ui.chat_message(), ui.interactive_image()), the ui.markdown() component does not provide or require a sanitize parameter, leaving applications vulnerable to XSS attacks. This vulnerability is fixed in 3.7.0.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-25516 since 02/02/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

By approaching the search of inurl:ui.html it is possible to find vulnerable targets with Google Hacking.

Upgrading to version 3.7.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-5566). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• zauberzeug

Name

• NiceGUI

Version

• 3.0
• 3.1
• 3.2
• 3.3
• 3.4
• 3.5
• 3.6

Website

• Product: https://github.com/zauberzeug/nicegui/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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