Environment variables are a set of dynamic named values that can affect the way running processes will behave on a computer. For example, an environment variable with a standard name can designate the location that a particular computer system uses to store temporary files but this may vary from one computer system to another.
Acunetix found an environmental variable listed on this page. This is common for debug/test pages that should not be available in production system.
Restrict access to this file or remove it from your system.