In Open Ticket Request System (OTRS) 3.3.x through 3.3.16, 4.x through 4.0.23, and 5.x through 5.0.19, an attacker with agent permission is capable of opening…

In Open Ticket Request System (OTRS) 3.3.x through 3.3.16, 4.x through 4.0.23, and 5.x through 5.0.19, an attacker with agent permission is capable of opening a specific URL in a browser to gain administrative privileges / full access. Afterward, all system settings can be read and changed. The URLs in question contain index.pl?Action=Installer with ;Subaction=Intro or ;Subaction=Start or ;Subaction=System appended at the end.