GHSA-mhpg-c27v-6mxr

Suggest an improvement
Source
https://github.com/advisories/GHSA-mhpg-c27v-6mxr
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/01/GHSA-mhpg-c27v-6mxr/GHSA-mhpg-c27v-6mxr.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-mhpg-c27v-6mxr
Published
2026-01-08T20:16:41Z
Modified
2026-01-08T20:29:47.460683Z
Severity
  • 7.2 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N CVSS Calculator
Summary
NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS
Details

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

  1. handleStateEvent emits sub_pages_open event.

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

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

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

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

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

  1. 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

  1. 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://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L206-L217

PoC

Just visiting this page (no click required), consistently triggers XSS in https://nicegui.io domain. 

<html>
  <body>
    <iframe id="myiframe" src="https://nicegui.io" width="100%" height="600px" onload="triggerXSS()"></iframe>
    <script>
      function triggerXSS() {
        if (!myiframe.src.includes("#")) {
          myiframe.src = "https://nicegui.io#x');alert(document.domain)//";
        }
      }
    </script>
  </body>
</html>

<img width="1429" height="643" alt="image" src="https://github.com/user-attachments/assets/310dbb5c-65d5-44f2-8417-dcf044829bc6" />

Impact

Any page which uses ui.sub_pages and does not actively prevent itself from being put in an iframe is affected.

The impact is high since by-default NiceGUI pages are iframe-embeddable with no native opt-out functionalities except by manipulating the underlying app via FastAPI methods, and that ui.sub_pages is actively promoted as the new modern way to create Single-Page Applications (SPA).

Patch

  1. Not use ui.sub_pages
  2. Block iframe with the following code 
    @app.middleware('http')
async def iframe_blocking_middleware(request, call_next):
    response = await call_next(request)
    response.headers['X-Frame-Options'] = 'DENY'
    return response

Appendix

AI is used safely to judge the CVSS scoring (input is censored).

Please find the results in https://poe.com/s/3FXuwp7TAYxqLomARXma

Scoring update after manual review

The scoring done by AI was quite biased. Upon further review it is less dramatic.

  • User Interaction None: There's almost no interaction required, and none of the interaction is with the vulnerable system.
  • Confidentiality & Integrity Low: The extent of data confidentiality & integrity loss is bounded by the highest priviledged user in the entire NiceGUI application. There does not exist a means of performing data manipulating tasks that said admin cannot already do.
  • Availability None: No DDoS is possible with this. Site remains performant as ever.
Database specific 
{
    "cwe_ids": [
        "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-08T20:16:41Z",
    "nvd_published_at": "2026-01-08T10:15:55Z",
    "severity": "HIGH"
}
References

Affected packages

PyPI / nicegui

Package

Name
nicegui
View open source insights on deps.dev
Purl
pkg:pypi/nicegui

Affected ranges

Type
ECOSYSTEM
Events
Introduced
2.22.0
Fixed
3.5.0

Affected versions

2.*

2.22.0
2.22.1
2.22.2
2.23.0
2.23.1
2.23.2
2.23.3
2.24.0
2.24.1
2.24.2

3.*

3.0.0rc1
3.0.0
3.0.1
3.0.2
3.0.3
3.0.4
3.1.0
3.2.0
3.3.0
3.3.1
3.4.0
3.4.1

Database specific

last_known_affected_version_range

"<= 3.4.1"

source

"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/01/GHSA-mhpg-c27v-6mxr/GHSA-mhpg-c27v-6mxr.json"