Description

Time-of-check Time-of-use (TOCTOU) Race Condition in league/flysystem

Impact

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:

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.

Patches

The unicode whitespace removal has been replaced with a rejection (exception).

The library has been patched in:

1.x: https://github.com/thephpleague/flysystem/commit/f3ad69181b8afed2c9edf7be5a2918144ff4ea32

2.x: https://github.com/thephpleague/flysystem/commit/a3c694de9f7e844b76f9d1b61296ebf6e8d89d74

Workarounds

For 1.x users, upgrade to 1.1.4. For 2.x users, upgrade to 2.1.1.

Mitigation

Aliases

References