alert tcp $HOME_NET any -> $EXTERNAL_NET ![25,443,587,9997] (msg:"ET MALWARE APT33/CharmingKitten Shellcode Communicating with CnC"; flow:established,to_server; dsize:<150; content:"|16 03|"; depth:2; content:"|00|"; distance:1; within:1; content:"|01 00 00|"; distance:1; within:3; content:"|03|"; distance:1; within:1; content:"|5b e0 37|"; distance:1; within:3; fast_pattern; content:"|00|"; distance:0; content:"|00|"; distance:1; within:1; content:"|00|"; distance:1; within:1; threshold:type limit, count 1, seconds 30, track by_dst; content:!"mtalk.google.com"; reference:md5,a60f127a06e5b3dcacd1ec346f7995c5; classtype:targeted-activity; sid:2026576; rev:4; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2018_11_05, deployment Perimeter, malware_family Shellcode, performance_impact Low, confidence High, signature_severity Major, tag APT33_CharmingKitten, tag Shellcode, updated_at 2020_07_16;)