alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"ET MALWARE PackClient Core startup probe state"; flow:established,to_client; content:"SYS|7c|Q|7c|EXT|7c|STARTUP|7c|PROBE|7c|"; fast_pattern; xbits:isset,ET.PackClient_RAT,track ip_pair; reference:url,ivanimmanuel-dev.github.io/PackClient/; reference:url,www.proofpoint.com/us/blog/threat-insight/carry-compromise-ta4922-packs-packclient; classtype:trojan-activity; sid:2072313; rev:1; metadata:affected_product Windows_XP_Vista_7_8_10_Server_32_64_Bit, affected_product Windows_11, attack_target Client_and_Server, tls_state plaintext, created_at 2026_10_01, deployment Perimeter, malware_family PackClient_RAT, performance_impact Low, confidence High, signature_severity Major, tag RAT, updated_at 2026_10_01, mitre_tactic_id TA0037, mitre_tactic_name Command_And_Control, mitre_technique_id T1041, mitre_technique_name Exfiltration_Over_C2_Channel;)