alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET MALWARE Cobalt Strike Activity (GET)"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"/oscp/"; startswith; fast_pattern; pcre:"/^[a-z]{256}$/R"; http.header_names; content:"|0d 0a|Accept|0d 0a|Host|0d 0a|User-Agent|0d 0a|Connection|0d 0a|Cache-Control|0d 0a 0d 0a|"; bsize:57; reference:url,www.cert.ssi.gouv.fr/cti/CERTFR-2021-CTI-009; reference:md5,f790bea81673806479e30337629fa605; classtype:trojan-activity; sid:2034358; rev:1; metadata:attack_target Client_Endpoint, created_at 2021_11_08, deployment Perimeter, deployment SSLDecrypt, malware_family Cobalt_Strike, confidence Medium, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2021_11_08;)