alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Win32/GRAT2 Client CnC Checkin"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/aboutus.aspx?"; startswith; pcre:"/^(?:[A-Za-z0-9\x2b\x2f\x3d]){15,25}$/R"; http.header_names; content:"User-Agent|0d 0a|Host|0d 0a|Connection|0d 0a 0d 0a|"; bsize:34; fast_pattern; http.connection; content:"Keep-Alive"; bsize:10; reference:url,github.com/r3nhat/GRAT2; reference:md5,3b8536686562848b63bb9143d3ca410a; classtype:command-and-control; sid:2038541; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, attack_target Client_Endpoint, created_at 2022_08_17, deployment Perimeter, malware_family GRAT2, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_08_17;)