An issue was discovered in Trend Micro InterScan Messaging Security (Virtual Appliance) 9.1-1600. An authenticated user can execute a terminal command in the context of the web server user (which is root). Besides, the default installation of IMSVA comes with default administrator credentials. The saveCert.imss endpoint takes several user inputs and performs blacklisting. After that, it uses them as arguments to a predefined operating-system command without proper sanitization. However, because of an improper blacklisting rule, it's possible to inject arbitrary commands into it.