CVE-2026-39844: Zauberzeug Nicegui

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

NiceGUI is a Python-based UI framework. Prior to 3.10.0, Since PurePosixPath only recognizes forward slashes (/) as path separators, an attacker can bypass this sanitization on Windows by using backslashes (\) in the upload filename. Applications that construct file paths using file.name (a pattern demonstrated in NiceGUI's bundled examples) are vulnerable to arbitrary file write on Windows. This vulnerability is fixed in 3.10.0.

Affected products

• Zauberzeug Nicegui: before 3.10.0 (fixed in 3.10.0)

Published 2026-04-08. Last modified 2026-07-24.