CVE-2026-39844

Awaiting Analysis Awaiting Analysis - Queue

Path Traversal in NiceGUI Allows Arbitrary File Write on Windows

Publication date: 2026-04-08

Last updated on: 2026-04-15

Assigner: GitHub, Inc.

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.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published

2026-04-08

Last Modified

2026-04-15

Generated

2026-07-06

AI Q&A

2026-04-09

EPSS Evaluated

2026-07-05

NVD

CVE-2026-39844

EUVD

EUVD-2026-20610

Affected Vendors & Products

Vendor	Product	Version / Range
zauberzeug	nicegui	to 3.10.0 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-22	The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

Executive Summary

This vulnerability exists in NiceGUI, a Python-based UI framework, in versions prior to 3.10.0. The issue arises because PurePosixPath only recognizes forward slashes (/) as path separators, but on Windows systems, backslashes (\) are used. An attacker can exploit this by using backslashes in an upload filename to bypass sanitization checks. If an application constructs file paths using the uploaded file's name (file.name), this can lead to arbitrary file write on Windows systems.

Impact Analysis

The vulnerability allows an attacker to write arbitrary files on a Windows system where the vulnerable NiceGUI version is used. This can lead to unauthorized modification or creation of files, potentially compromising the integrity of the system or application.

Mitigation Strategies

To mitigate this vulnerability, upgrade NiceGUI to version 3.10.0 or later, where the issue with path sanitization on Windows has been fixed.

Hi! I’m here to help you understand CVE-2026-39844. Ask me anything about the vulnerability, its impact, or mitigation strategies.

0/70