What’s Vulnerable › Vulnerabilities

CVE-2026-39844: NiceGUI has a Path Traversal in NiceGUI Upload Filename on Windows via Backslash Bypass of PurePosixPath Sanitization

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-08 · updated 2026-07-24
• Weakness: CWE-22

Description

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

How to fix

Upgrade to a fixed version: zauberzeug nicegui 3.10.0. Check the vendor advisory for mitigations.

References

• https://github.com/zauberzeug/nicegui/commit/d38a702e3af2da5b0708f689be8d71413fc77056
• https://github.com/zauberzeug/nicegui/releases/tag/v3.10.0
• https://github.com/zauberzeug/nicegui/security/advisories/GHSA-w8wv-vfpc-hw2w

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