ET RETIRED Possible LINE RUNNER Backdoor Connection Attempt

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET RETIRED Possible LINE RUNNER Backdoor Connection Attempt";
    flow:established,to_server;
    http.method;
    content:"GET";
    http.uri;
    content:"/+CSCOE+/portal.css?"; fast_pattern; startswith;
    content:"|3d|"; distance:0;
    content:"|26|"; distance:0;
    content:"|3d|"; distance:0;
    http.header_names;
    content:!"|0d 0a|Referer|0d 0a|";
    reference:url,www.cyber.gc.ca/en/news-events/cyber-activity-impacting-cisco-asa-vpns;
    classtype:trojan-activity;
    sid:2052270; rev:2;
    metadata:affected_product Cisco_ASA, attack_target Networking_Equipment, tls_state TLSDecrypt, created_at 2024_04_25, deployment Perimeter, deployment SSLDecrypt, former_category MALWARE, malware_family LINE_RUNNER, performance_impact Low, confidence Low, signature_severity Major, updated_at 2024_10_04, reviewed_at 2024_10_04;
    target:dest_ip;
)