The most common weakness of Intrusion Detection and Prevention System is encrypted traffic inspection. The SSH encrypted traffic requires private/public keys for encryption/decryption and it is very hard to obtain the private key from attackers.
Solution
How we can do that? If you are running Suricata as IPS, SSH Dynamic, Reverse and Port Forwarding tunnel will be detected by the following rules :
# ssh (port 5228=Google Talk, port 6697=IRC)
alert tcp any any -> any 22 (msg:"LOCAL SSH connect"; flow:established,to_server; app-layer-protocol:ssh; sid:1000008; rev:1;)
drop tcp any any -> any 22 (msg:"LOCAL not SSH but Port 22"; flow:established,to_server; app-layer-protocol:!ssh; sid:1000009; rev:1;)
drop tcp any any -> any ![22,5228,6697] (msg:"LOCAL SSH but not Port 22"; flow:established,to_server; app-layer-protocol:ssh; sid:1000010; rev:1;)The first rule will alert you that there is a SSH connection to the port 22. The second rule will block the traffic the not SSH protocol but connect to port 22. The last rule will block the SSH connection that are not connecting to port 22, 5228 or 6697, where port 5228 is Google Talk and port 6697 is IRC.
If you do not use standard port 22 for SSH, please change the value when necessary.
Reference
SSH Brute Force and Suricata
Protocol Anomalies Detection
That's all! See you.
