alert tls $EXTERNAL_NET any -> $HOME_NET any (
msg:"ET INFO Possible JARM Fingerprinting Client Hello via tls1_3_invalid";
flow:established,to_client;
content:"|16 03 01|"; startswith;
content:"|00 16 00 33 00 67 c0 9e c0 a2 00 9e 00 39 00 6b c0 9f c0 a3 00 9f 00 45 00 be 00 88 00 c4 00 9a c0 08 c0 09 c0 23 c0 ac c0 ae c0 2b c0 0a c0 24 c0 ad c0 af c0 2c c0 72 c0 73 cc a9 cc 14 c0 07 c0 12 c0 13 c0 27 c0 2f c0 14 c0 28 c0 30 c0 60 c0 61 c0 76 c0 77 cc a8 cc 13 c0 11 00 0a 00 2f 00 3c c0 9c c0 a0 00 9c 00 35 00 3d c0 9d c0 a1 00 9d 00 41 00 ba 00 84 00 c0 00 07 00 04 00 05|"; fast_pattern;
content:"|08|http/0.9|08|http/1.0|08|http/1.1|06|spdy/1|06|spdy/2|06|spdy/3|02|h2|03|h2c|02|hq";
content:"|03 01 03 02 03 03 03 04|"; endswith;
reference:url,engineering.salesforce.com/easily-identify-malicious-servers-on-the-internet-with-jarm-e095edac525a;
classtype:misc-activity;
sid:2036699; rev:1;
metadata:created_at 2022_05_25, confidence High, signature_severity Informational, tag Description_Generated_By_Proofpoint_Nexus, updated_at 2022_05_25;
)