Source(s) :

• Emerging Threats SIG 2001219
• Emerging Threats SIG 2006546
• Emerging Threats SIG 2006435
• Wikipedia Brute Force Attack
• SSH library

We have compile a list of more of 5 000 user name how have been used to try to brute force login our HoneyNet servers. This list is updated every day.

Emerging Threats SIG 2001219 create an alert if we have 5 destination port 22/TCP connexions during the interval of 120 seconds. If we see, for example, 10 connexions during the interval of 120 seconds, 2 alerts will be triggered. This SIG could be used to detect SSH Brute Force Attack.

Emerging Threats SIG 2006546 create an alert if the content of the packet in destination of port 22/TCP contain “SSH-” and “libssh”. In addition the alert is triggered if we detect 5 connexions during the interval of 30 seconds. If we see, for example, 10 connexions during the interval of 30 seconds, only 1 alert will be triggered. This SIG could be used to detect SSH Brute Force Attack, but based on strict recognition of tools how are using “libssh”.

Emerging Threats SIG 2006345 create an alert if the content of the packet in destination of port 22/TCP contain “SSH-” and “libssh”. In addition the alert is triggered if we detect 1 connexion during the interval of 30 seconds. If we see, for example, 10 connexions during the interval of 30 seconds, only 1 alert will be triggered. This SIG could be used to detect SSH fingerprinting, but based on strict recognition of tools how are using “libssh”. This SIG is not useful for SSH Brute Force Attack recognition due to the limit type threshold.

In parallel you could correlate theses alerts with your firewall logs and / or SSH daemon logs, to create a real correlated alert. But still the attacker is not logged in your system, these alerts should not have a high priority level, cause most of time these scans are done by bots. Maybe you could add the attacker IP address in a “Suspicious Attacker” list for furthers trends and correlations activities.

Another operation you could do, is to compare the username provided from the SSH brute forcing dictionary with yours existing SSH usernames. If your username is present into the dictionary, we recommend you to change it.