Modeling network attacks for scenario construction

The Intrusion detection system (IDS) is a security technology that attempts to identify network intrusions. Defending against multistep intrusions which prepare for each other is a challenging task. In this paper, the Context-Free Grammar (CFG) was used to describe the multistep attacks using alerts classes. Based on the CFCs, the modified LR parser was employed to generate the parse trees of the scenarios presented in the alerts. Instead of searching all the received alerts for those that prepare for a new alert, we only search for the latest alert's type of each scenario. Consequently, the proposed system has an attractive time complexity. The experiments were performed on two different sets of network traffic traces, using different open-source and commercial IDSs. The detected scenarios are represented by Correlation Graphs (CGs). The experimental results show that the CFG can describe multistep attacks explicitly and the modified LR parser, based on the CFG, can construct scenarios successfully.