CVE-2026-21873

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{}

{"analysis": {"en": {"generated_at": "2026-04-18T07:44:27.626309+00:00", "value": {"mitigation_remediation": ["Upgrade NiceGUI to version 3.5.0 or later to eliminate the fault in the pushstate listener.", "If an upgrade cannot be performed immediately, remove or disable the use of ui.sub_pages in the application to prevent the vulnerable fragment manipulation.", "Implement a strict Content Security Policy that disallows inline scripts and unsafe eval features to mitigate the impact of any remaining XSS vectors."], "summary": {"action": "Immediate Patch", "impact": "Cross\u2011Site Scripting (XSS)"}, "threat_synthesis": {"affected_systems": "Applications built with Zauberzeug NiceGUI versions from 2.22.0 up to 3.4.1 that use ui.sub_pages are affected. All such deployments are vulnerable regardless of the host or domain, as the flaw resides in the framework\u2019s client\u2011side code.", "description_and_impact": "NiceGUI, a Python UI framework, contains an unsafe pushstate event listener used by ui.sub_pages. The listener incorrectly handles changes to the fragment identifier of the URL. An attacker can exploit this flaw by loading the application in a cross\u2011site iframe and manipulating the fragment without user interaction. The result is a zero\u2011click XSS vulnerability that can inject arbitrary script into the victim\u2019s browser, enabling session hijacking, credential theft, or defacement of the application.", "risk_and_exploitability": "The CVSS score of 7.2 indicates moderate\u2011to\u2011high severity. The EPSS score is below 1%, suggesting a low likelihood of widespread exploitation at present, and the vulnerability is not listed in the CISA KEV catalog. However, because the flaw can be triggered without any user interaction from a cross\u2011site iframe, it is effectively zero\u2011click and can be executed by remote attackers who control a malicious site. The patch was released in NiceGUI 3.5.0; lacking the fix an attacker can simply craft a malicious page that embeds the target application and sets the fragment identifier to trigger script injection."}}}}, "created": "2026-01-09T13:25:32.207541+00:00", "updated": "2026-04-18T07:45:24.985441+00:00", "vendors": ["zauberzeug", "zauberzeug$PRODUCT$nicegui"]}