The Horde/IMP package (3.1.7-3.3.2) that is shipped with Plesk v. 8.x and earlier versions of 9.x (before 9.5.4) has a vulnerability that allows an attacker to run malicious software by passing the login to the webmail with a POST request to the /horde/imp/redirect.php file that includes the PHP code as the username. For example

This results in the PHP code being logged to the /var/log/psa-horde/psa-horde.log file, which, due to a vulnerability in the barcode.php file, allows attackers to cause Horde to execute the code by making this request:
Plesk versions affected: