alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE Possible UNC1878/FIN12 Cobalt Strike CnC SSL Cert Inbound (office)"; flow:established,to_client; tls.cert_subject; content:"C=US, ST="; startswith; content:", O=Office, OU=, CN="; nocase; fast_pattern; tls.cert_issuer; content:"C=US, ST="; startswith; content:", O=Office, OU=, CN="; nocase; reference:md5,880a45ff31bc540e80ecf2cf93134c12; reference:url,gist.github.com/aaronst/6aa7f61246f53a8dd4befea86e832456; reference:url,www.youtube.com/watch?v=BhjQ6zsCVSc; classtype:targeted-activity; sid:2031134; rev:3; metadata:attack_target Client_Endpoint, created_at 2020_10_29, deployment Perimeter, malware_family Cobalt_Strike, performance_impact Low, confidence Medium, signature_severity Major, tag SSL_Malicious_Cert, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2020_11_19;)