ET MALWARE Cobalt Strike Malleable C2 Profile (__session__id Cookie)

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE Cobalt Strike Malleable C2 Profile (__session__id Cookie)";
    flow:established,to_server;
    http.cookie;
    content:"__session__id="; startswith; fast_pattern;
    pcre:"/^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{4})$/R";
    http.header_names;
    content:!"Referer";
    reference:url,twitter.com/Unit42_Intel/status/1387149833274810368;
    reference:url,github.com/pan-unit42/tweets/blob/master/2021-04-26-IcedID-with-Cobalt-Strike-IOCs.txt;
    classtype:command-and-control;
    sid:2032965; rev:1;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2021_05_17, deployment Perimeter, malware_family Cobalt_Strike, confidence Medium, signature_severity Major, updated_at 2021_05_17, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1001, mitre_technique_name Data_Obfuscation;
)