CVE-2026-39844

NiceGUI has a Path Traversal in NiceGUI Upload Filename on Windows via Backslash Bypass of PurePosixPath Sanitization

CVSS 5.9 MEDIUMEPSS 0.4%CWE-22

Vexday Risk Score

13Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 5.9EPSS 0.4%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

08 Apr 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

zauberzeug · nicegui

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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