Well, $_SERVER is a special array which is called a SUPERGLOBAL. It’s not really supposed to be used
for general use. It is used to acquire settings in the server system.
Here is a link that talks about a couple exploits that can occur…
https://markjaquith.wordpress.com/2009/09/21/php-server-vars-not-safe-in-forms-or-links/
There are many others, but, here is just one more that talks about it.
http://www.mc2design.com/blog/article/serverphp_self-can-not-be-trusted-but-there-are-safe-alternatives
Everything is safe if you prepare for it. But, some PHP arrays are for special uses only. Not sure if this
really answers you or not, but, gives you some viewpoints of others. Hope it helps a little…
PS: you can always private-message Strider64 and ask him for more complete info…