FacturaScripts is an open source accounting and invoicing software. Versions 2026 and below contain a critical vulnerability in the Plugins::add() function. The system fails to properly validate the file paths within uploaded ZIP archives. This allows an attacker to perform a Zip Slip attack, leading to Arbitrary File Write and Remote Code Execution (RCE) by overwriting sensitive .php files outside the designated plugins directory. The vulnerability is located in Plugins.php. While the testZipFile function attempts to validate that the ZIP contains only one root folder, it does not sanitize or validate the individual file paths within that folder. An attacker can bypass this check by naming a file ValidPluginName/../../shell.php. The explode function will see ValidPluginName as the root folder, satisfying the count($folders) != 1 check. However, during extraction, the ../../ sequence triggers a path traversal, allowing the file to be written anywhere the web server has permissions the root directory. This issue is fixed in version 2026.1.