alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Grizzly Loader CnC Checkin (POST)"; flow:established,to_server; http.method; content:"POST"; http.uri; bsize:12; pcre:"/^\x2f(?:[a-zA-Z0-9]{5})\x2fevent$/"; http.header_names; content:"|0d 0a|x-timestamp|0d 0a|x-nonce|0d 0a|x-signature|0d 0a|x-request-context|0d 0a|"; nocase; fast_pattern; classtype:command-and-control; sid:2071861; rev:1; metadata:affected_product Windows_Client, attack_target Client_Endpoint, tls_state TLSDecrypt, created_at 2026_08_31, deployment Perimeter, deployment SSLDecrypt, malware_family GrizzlyLoader, confidence High, signature_severity Critical, tag c2, updated_at 2026_08_31, mitre_tactic_id TA0011, mitre_tactic_name Command_And_Control, mitre_technique_id T1071, mitre_technique_name Application_Layer_Protocol; target:src_ip;)