alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET INFO Possible Psiphon Proxy Tool traffic"; flow:established,to_server; urilen:1; http.method; content:"POST"; http.cookie; pcre:"/^[A-Z]=(?:[A-Za-z0-9+/])+=?=?$/"; http.accept_enc; content:"gzip"; startswith; http.content_type; bsize:24; content:"application/octet-stream"; fast_pattern; nocase; http.header_names; to_lowercase; content:"content-length|0d 0a|"; content:!"|0d 0a|user-agent|0d 0a|"; content:!"|0d 0a|referer|0d 0a|"; content:!"|0d 0a|connection|0d 0a|"; content:!"|0d 0a|cache-control|0d 0a|"; content:!"|0d 0a|accept|0d 0a|"; threshold:type threshold, track by_src, count 20, seconds 120; reference:md5,a050a1e9fa0fe0e01cfbf14ead388c4e; classtype:policy-violation; sid:2022679; rev:9; metadata:created_at 2016_03_28, confidence Medium, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2024_05_04;)