Vulnerability · Published Jan 8, 2026 · Assigned by GitHub_M

CVE-2026-21873Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`

High 7.2

In plain English

A high-severity cross-site scripting in nicegui from zauberzeug. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.2High

Exploit odds (30 days)0.3%top 82.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
PyPI	nicegui	3.5.0	GHSA-mhpg-c27v-6mxr
PyPI	nicegui	3.5.0	PYSEC-2026-1702

Affected products (as reported)

Vendor	Product	Versions
zauberzeug	nicegui	>= 2.22.0, < 3.5.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

References

https://github.com/zauberzeug/nicegui/security/advisories/GHSA-mhpg-c27v-6mxr x_refsource_CONFIRM
https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0 x_refsource_MISC