Detection of SSH Brute Force Attacks Using Aggregated Netflow Data

The SSH Brute force attack is one of the most prevalent attacks in computer networks. These attacks aim to gain ineligible access to users' accounts by trying plenty of different password combinations. The detection of this type of attack at the network level can overcome the scalability issue of host-based detection methods. In this paper, we provide a machine learning approach for the detection of SSH brute force attacks at the network level. Since extracting discriminative features for any machine learning task is a fundamental step, we explain the process of extracting discriminative features for the detection of brute force attacks. We incorporate domain knowledge about SSH brute force attacks as well as the analysis of a representative collection of the data to define the features. We collected real SSH traffic from a campus network. We also generated some failed login data that a legitimate user who has forgotten his/her password can produce as normal traffic that can be similar to the SSH brute force attack traffic. Our inspection on the collected brute force Netflow data and the manually produced SSH failed login data showed that the Netflow features are not discriminative enough to discern brute force traffic from the failed login traffic produced by a legitimate user. We introduced an aggregation of Netflows to extract the proper features for building machine learning models. Our results show that the models built upon these features provide excellent performances for the detection of brute force attacks.