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

5.9MEDIUM

Key Information:

Vendor

Zauberzeug

Status
Nicegui
Vendor
CVE Published:
8 April 2026

What is CVE-2026-39844?

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 Version(s)

nicegui < 3.10.0

References

https://github.com/zauberzeug/nicegui/security/advisories...
x_refsource_CONFIRM
https://github.com/zauberzeug/nicegui/commit/d38a702e3af2...
x_refsource_MISC
https://github.com/zauberzeug/nicegui/releases/tag/v3.10.0
x_refsource_MISC

CVSS V3.1

Score:
5.9
Severity:
MEDIUM
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.