Summary
An unsafe implementation in the click event listener used by ui.sub_pages, combined with attacker-controlled link rendering on the page, causes an XSS when the user actively clicks on the link.
Details
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On click, eventually sub_pages_navigate event is emitted.
https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L41-L63
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SubPagesRouter (used by ui.sub_pages), lisnening on sub_pages_navigate, _handle_navigate runs.
https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22
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_handle_navigate runs run_javascript with f-string substituting self.current_path which is simply surrounded by double-quotes. The string context can be broken out easily.
https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L73-L88
PoC
The minimal PoC boils down to this:
from nicegui import ui
ui.sub_pages({'/': lambda: ui.link('Go to XSS', '/"+alert(1)+"')})
ui.run()However, it is more likely that the attack takes place with attacker-controlled input, for which this shows it:
from nicegui import app, ui
ui.sub_pages({'/': lambda: ui.label('Hello, World!')})
ui.textarea('Markdown content').bind_value(app.storage.general, 'markdown_content')
ui.markdown().bind_content_from(app.storage.general, 'markdown_content')
ui.run()Vulnerable input is [XSS LINK](/"+alert(document.domain)+") (causes double payload execution, though)
Both cases require someone to click on the link.
Impact
Any page which uses ui.sub_pages and renders arbitrary links on screen (common case of ui.markdown) is affected.
The impact is low since a click is always required from the user, who can on-hover to discover the sketchy content of the link and stop if well-trained.
Appendix
AI is used safely to judge the CVSS scoring (input is not even provided, just the impact statement).
Please find the results in https://poe.com/s/y5DvyqgtszDGLUuHin1O
Scoring update after manual review
- Scope Changed is more inline with other posted XSS vulnerabilities
- Availability None: No DDoS is possible with this. Site remains performant as ever.
References
evnchn Reporter
xx-mikusan-xx Reporter
falkoschindler Remediation reviewer
Summary
An unsafe implementation in the
clickevent listener used byui.sub_pages, combined with attacker-controlled link rendering on the page, causes an XSS when the user actively clicks on the link.Details
On
click, eventuallysub_pages_navigateevent is emitted.https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L41-L63
SubPagesRouter (used by ui.sub_pages), lisnening on
sub_pages_navigate,_handle_navigateruns.https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22
_handle_navigaterunsrun_javascriptwith f-string substitutingself.current_pathwhich is simply surrounded by double-quotes. The string context can be broken out easily.https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L73-L88
PoC
The minimal PoC boils down to this:
However, it is more likely that the attack takes place with attacker-controlled input, for which this shows it:
Vulnerable input is
[XSS LINK](/"+alert(document.domain)+")(causes double payload execution, though)Both cases require someone to click on the link.
Impact
Any page which uses
ui.sub_pagesand renders arbitrary links on screen (common case ofui.markdown) is affected.The impact is low since a click is always required from the user, who can on-hover to discover the sketchy content of the link and stop if well-trained.
Appendix
AI is used safely to judge the CVSS scoring (input is not even provided, just the impact statement).
Please find the results in https://poe.com/s/y5DvyqgtszDGLUuHin1O
Scoring update after manual review
References