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EUVD-2026-265157

2026-10-06T17:44:09.637756+00:00

EUVD-2026-265157

fkie_cve-2026-21873

2026-10-06T17:44:09.637793+00:00

NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.

GHSA-mhpg-c27v-6mxr — NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS

2026-10-06T17:44:09.637827+00:00

Affected: PyPI: nicegui

### Summary

An unsafe implementation in the `pushstate` event listener used by `ui.sub_pages` allows an attacker to manipulate the fragment identifier of the URL, which _they can do despite being cross-site, using an iframe_.

### Details

The problem is traced as follows:

1. On `pushstate`, `handleStateEvent` is executed.

https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L38-L39

2. `handleStateEvent` emits `sub_pages_open` event.

https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L22-L25

3. `SubPagesRouter` (used by `ui.sub_pages`), lisnening on `sub_pages_open`, `_handle_open` runs.

https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22

4. `_handle_open` finds any `SubPages` and runs `_show()` on them

https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L63-L71

5. If the if-logic is followed or debug prints are added, it can be found that it calls `self._handle_scrolling(match, behavior='smooth')` directly

https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L76-L100

6. **CULPRIT** `_handle_scrolling` runs `_scroll_to_fragment` as there is a fragment, which runs vulnerable JS if the `fragment` (attacker-controlled) escapes out of the quotes.

https:…

PYSEC-2026-1702 — NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS

2026-10-06T17:44:09.637883+00:00