CVE-2026-21873: PYSEC-2026-1702 - NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS

CVE-2026-21873 · Severity: low · CVSS 3.1 · Published 2026-07-07

NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS

Technologies: nicegui (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-21873 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-21873 being exploited in the wild.
How severe is CVE-2026-21873?
Low severity, with a CVSS score of 3.1, published 7 July 2026.
Which products and versions are affected?
nicegui (PyPI) ECOSYSTEM:introduced=2.22.0,fixed=3.5.0.
Is there a fix for CVE-2026-21873?
Yes. nicegui (PyPI): upgrade to 3.5.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-21873?
Check whether you run nicegui (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • nicegui (PyPI): upgrade to 3.5.0 or later
    pip install "nicegui>=3.5.0"

Affected products

  • nicegui (PyPI) ECOSYSTEM:introduced=2.22.0,fixed=3.5.0

Identifiers

  • CVE-2026-21873
  • GHSA-mhpg-c27v-6mxr
  • PYSEC-2026-1702

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