alert tls $EXTERNAL_NET any -> $HOME_NET any (msg:"ET POLICY [Fidelis] Abnormal x509v3 SubjectKeyIdentifier extension"; flow:established,to_client; dsize:>768; content:"|16 03|"; depth:2; content:"|06 03 55 1d 0e 04|"; offset:336; pcre:"/^.\x04[^\x08\x10\x14\x20\x30\x40]/R"; threshold:type limit, track by_src, seconds 30, count 1; reference:url,www.fidelissecurity.com/threatgeek/2018/02/exposing-x509-vulnerabilities; classtype:misc-attack; sid:2025319; rev:4; metadata:attack_target Client_Endpoint, created_at 2018_02_06, deployment Perimeter, performance_impact Significant, confidence High, signature_severity Major, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_04_23;)