NiceGUI apps are vulnerable to XSS which uses ui.sub_pages and render arbitrary user-provided links

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-21872: 0.27% estimated exploitation activity in the next 30 days; percentile 19.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary An unsafe implementation in the click event listener used by ui.subpages, 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 subpagesnavigate event is emitted. https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/subpages.js#L41-L63 2. SubPagesRouter (used by ui.subpages), lisnening on subpagesnavigate, handlenavigate runs. https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/subpagesrouter.py#L18-L22 3. handlenavigate runs runjavascript with f-string substituting self.currentpath which is simply surrounded by double-quotes. The string context can be broken out easily. https://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/subpagesrouter.py#L73-L88 PoC The minimal PoC boils down to this: However, it is more likely that the attack takes place with…

Published by the source

8 Jan 2026, 20:08 UTC

Last modified by the source

7 Jul 2026, 17:56 UTC

Source last checked

26 Oct 2026, 13:36 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m7j5-rq9j-6jj9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-m7j5-rq9j-6jj9

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# Patch Next advisory brief: CVE-2026-21872

Advisory: NiceGUI apps are vulnerable to XSS which uses `ui.sub_pages` and render arbitrary user-provided links
IDs: CVE-2026-21872, GHSA-m7j5-rq9j-6jj9
Record: https://patchnext.com/advisories/cve-2026-21872 (revision 2, source checked 26 Oct 2026, 13:36 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nicegui 3.5.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI nicegui: affected >= 2.22.0, <= 3.4.1; fixed in 3.5.0

## Suggested inspection (read-only)
- `python -m pip show nicegui`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nicegui.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-m7j5-rq9j-6jj9 (OSV record GHSA-m7j5-rq9j-6jj9 lists affected ranges: PyPI nicegui >=2.22.0 <3.5.0 (fixed))
- Verified: https://github.com/advisories/GHSA-m7j5-rq9j-6jj9 (GitHub-reviewed advisory GHSA-m7j5-rq9j-6jj9 lists affected ranges: PyPI nicegui >=2.22.0 <=3.4.1)

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