DEPCOMM: Graph Summarization on System Audit Logs for Attack Investigation

Causality analysis generates a dependency graph from system audit logs, which has emerged as an important solution for attack investigation. In the dependency graph, nodes represent system entities (e.g., processes and files) and edges represent dependencies among entities (e.g., a process writing to a file). Despite the promising early results, causality analysis often produces a large graph (> 100,000 edges) and it is a daunting task for security analysts to inspect such a large graph for attack investigation. To address challenges in attack investigation, we propose DEPCOMM, a graph summarization approach that generates a summary graph from a dependency graph by partitioning a large graph into process-centric communities and presenting summaries for each community. Specifically, each community consists of a set of intimate processes that cooperate with each other to accomplish certain system activities (e.g., file compression), and the resources (e.g., files) accessed by these processes. Within a community, DEPCOMM further identifies redundant edges caused by less-important and repetitive system activities, and perform compression on these edges. Finally, DEPCOMM generates the summary for each community using the InfoPaths that represent the information flows across communities. These InfoPaths are more likely to capture a set of attack-related processes that work together to achieve certain malicious goals. Our evaluations on real attacks (\sim 150 million events) demonstrate that DEPCOMM generates 18.4 communities on average for a dependency graph, which is \sim 70 × smaller than the original graph. Our compression further reduces the edges in each community to 32.1 on average. Compared with the 9 state-of-the-art community detection algorithms, on average, DEPCOMM achieves a 2.29× better F1-score than these algorithms in detecting communities. Through cooperating with the automatic techniques HOLMES, DEPCOMM can identify attack-related communities by a recall of 96.2%. Our case studies on the real attacks also demonstrate DEPCOMM's effectiveness in facilitating attack investigation.