What’s Vulnerable › Vulnerabilities

CVE-2021-32708: Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem

Description

Flysystem is an open source file storage library for PHP. The whitespace normalisation using in 1.x and 2.x removes any unicode whitespace. Under certain specific conditions this could potentially allow a malicious user to execute code remotely. The conditions are: A user is allowed to supply the path or filename of an uploaded file, the supplied path or filename is not checked against unicode chars, the supplied pathname checked against an extension deny-list, not an allow-list, the supplied path or filename contains a unicode whitespace char in the extension, the uploaded file is stored in a directory that allows PHP code to be executed. Given these conditions are met a user can upload and execute arbitrary code on the system under attack. The unicode whitespace removal has been replaced with a rejection (exception). For 1.x users, upgrade to 1.1.4. For 2.x users, upgrade to 2.1.1.

Affected products

How to fix

Upgrade to a fixed version: thephpleague flysystem 1.1.4, 2.1.1; Packagist League/Flysystem 1.1.4, 2.1.1. Check the vendor advisory for mitigations.

References

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