ET POLICY Possible Autodiscover Credentials Leak via Basic Auth

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"ET POLICY Possible Autodiscover Credentials Leak via Basic Auth";
    flow:established,to_server;
    http.method;
    content:"GET";
    http.uri;
    content:"/autodiscover/autodiscover.xml"; nocase; fast_pattern;
    http.header;
    content:"Authorization|3a 20|Basic|20|";
    reference:url,guardicore.com/labs/autodiscovering-the-great-leak/;
    classtype:policy-violation;
    sid:2034019; rev:1;
    metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_and_Server, created_at 2021_09_23, deployment Perimeter, confidence High, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2021_09_23;
)