CVE-2026-21873
HighSummary
NiceGUI versions 2.22.0 to 3.4.1 have an unsafe implementation in the pushstate event listener used by ui.sub_pages, allowing an attacker to manipulate the fragment identifier of the URL, even cross-site, using an iframe. This issue has been patched in version 3.5.0.
Risk Assessment
Risk of URL manipulation and potential phishing or session hijacking attacks.
Recommendation
Update NiceGUI to version 3.5.0 or later to fix the vulnerability.
Other vulnerabilities in NiceGUI
See all- CVE-2026-45554Medium
NiceGUI is a Python-based UI framework. Prior to version 3.12.0, two FastAPI routes that serve per-component static assets in NiceGUI accept a sub-path parameter that may resolve to a directory rather than a file. Requests that resolve to a directory raise an unhandled RuntimeError inside Starlette's FileResponse, which Uvicorn writes to the server log as a full traceback. Because the routes are reachable without authentication, a remote attacker can amplify log volume and consume disk and log-pipeline capacity on any publicly reachable NiceGUI server. This issue has been patched in version 3.12.0.
- CVE-2026-45553High
NiceGUI prior to version 3.12.0 has a vulnerability in ui.restructured_text() that renders reStructuredText server-side without disabling file insertion directives. An attacker can read local files accessible to the NiceGUI server process.
- CVE-2026-39844Medium
NiceGUI, a Python-based UI framework, prior to version 3.10.0 is vulnerable to arbitrary file write on Windows. Because PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass sanitization by using backslashes (\) in the upload filename.
Original NVD description (English source)
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.