alert http $EXTERNAL_NET any -> $HTTP_SERVERS any (msg:"ET WEB_SERVER Possible Encrypted Webshell Download"; flow:established,to_client; file_data; content:"eval"; content:"mcrypt_decrypt"; within:30; reference:url,blog.sucuri.net/2013/10/backdoor-evasion-using-encrypted-content.html; classtype:bad-unknown; sid:2017640; rev:4; metadata:affected_product PHP, attack_target Web_Server, created_at 2013_10_28, deployment Datacenter, performance_impact Low, confidence Medium, signature_severity Major, updated_at 2020_08_19;)