ET MALWARE Possible Covenant Framework Grunt Stager HTTP Download (DynamicInvoke)

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Possible Covenant Framework Grunt Stager HTTP Download (DynamicInvoke)";
    flow:established,to_client;
    file_data;
    content:"toStream(assembly_str)";
    content:"delegate.DynamicInvoke(array.ToArray()).CreateInstance("; distance:0; fast_pattern;
    reference:url,github.com/cobbr/Covenant;
    reference:url,posts.specterops.io/entering-a-covenant-net-command-and-control-e11038bcf462;
    classtype:trojan-activity;
    sid:2027796; rev:1;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2019_08_04, deployment Perimeter, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2019_08_04;
)