ET MALWARE Fake Browser Update via Error Page Payload

alert http $EXTERNAL_NET any -> $HOME_NET any (
    msg:"ET MALWARE Fake Browser Update via Error Page Payload";
    flow:established,to_client;
    http.response_body;
    content:"let|20|agent|20 3d 20|navigator|2e|userAgent|2e|toLowerCase|28 29 3b|"; startswith; fast_pattern;
    content:"let|20|payload|5f|chrome|20 3d 20 27|"; distance:0;
    content:"let|20|payload|5f|firefox|20 3d 20 27|"; distance:0;
    content:"let|20|ua1|20 3d 20 27 27 3b|"; distance:0;
    content:"let|20|payload|20 3d 20 27 27 3b|"; distance:0;
    reference:url,isc.sans.edu/diary/Supply%20Chain%20Compromise%20or%20False%20Positive%3A%20The%20Intriguing%20Case%20of%20efile.com%20%5Bupdated%20-%20confirmed%20malicious%20code%5D/29708;
    classtype:trojan-activity;
    sid:2044885; rev:1;
    metadata:attack_target Client_Endpoint, created_at 2023_04_04, deployment Perimeter, performance_impact Low, confidence High, signature_severity Major, tag compromised_website, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2023_04_04;
)