alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Psiphon VPN Related Activity (POST)"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/"; bsize:1; http.header_names; content:"|0d 0a|Content-Length|0d 0a|Content-Type|0d 0a|Cookie|0d 0a|Accept-Encoding|0d 0a 0d 0a|"; fast_pattern; content:!"Referer"; http.content_type; content:"application/octet-stream"; bsize:24; http.cookie; pcre:"/^[A-Z]=[A-Za-z/+0-9=]{200,400}$/"; reference:md5,912e361d280d881980caca25cd0b80d4; classtype:bad-unknown; sid:2037033; rev:1; metadata:attack_target Client_Endpoint, created_at 2022_06_17, deployment Perimeter, performance_impact Moderate, confidence High, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_06_17;)