alert http $EXTERNAL_NET any -> $HTTP_SERVERS any (msg:"ET WEB_SERVER PHP WebShell Embedded In GIF (INBOUND)"; flow:established,from_server; file_data; content:"GIF89"; within:5; content:"<?php"; fast_pattern; distance:0; reference:url,blog.spiderlabs.com/2013/10/hiding-webshell-backdoor-code-in-image-files.html; classtype:successful-admin; sid:2017607; rev:2; metadata:created_at 2013_10_17, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_07_26;)