ET MALWARE Possible APT28 Xtunnel Activity

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET MALWARE Possible APT28 Xtunnel Activity";
    flow:established,to_server;
    http.method;
    content:"GET";
    http.uri.raw;
    pcre:"/^\/(?:\w+\/){1,5}\?[a-z]{1,6}=[a-z0-9]{2,40}(?:&[a-z]{1,6}=(?:[a-z0-9]){1,40}(%3D){0,2}){1,4}$/i";
    http.header;
    content:"deflate,sdch|0d 0a|Accept|3a 20|text|2f|html,application|2f|xhtml"; fast_pattern;
    http.user_agent;
    content:"Mozilla|2f|4.0|20 28|compatible|3b 20|MSIE|20|7.0";
    http.connection;
    content:"Close";
    http.header_names;
    content:!"Referer";
    content:!"Cache";
    classtype:targeted-activity;
    sid:2027405; rev:4;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, created_at 2019_05_30, deployment Perimeter, malware_family XTunnel, performance_impact Low, confidence Medium, signature_severity Major, tag APT, updated_at 2020_11_03;
)