GHSA-m7j5-rq9j-6jj9 NiceGUI apps are vulnerable to XSS which uses `ui.sub_pages` and render arbitrary user-provided links

• PyPI nicegui: >= 2.22.0, < 3.5.0 → fixed in 3.5.0

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 1. On `click`, eventually `sub_pages_navigate` event is emitted. https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L41-L63 2. 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 3. `_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: ```py 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: ```py 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+")` (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.