Malicious Office Macro Detection: Combined Features with Obfuscation and Suspicious Keywords

Abstract

Microsoft has implemented several measures to defend against macro viruses, including the use of the Antimalware Scan Interface (AMSI) and automatic macro blocking. Nevertheless, evidence shows that threat actors have found ways to bypass these mechanisms. As a result, phishing emails continue to utilize malicious macros as their primary attack method. In this paper, we analyze 77 obfuscation features from the attacker’s perspective and extract 46 suspicious keywords in macros. We first combine the aforementioned two types of features to train machine learning models on a public dataset. Then, we conduct the same experiment on a self-constructed dataset consisting of newly discovered samples, in order to verify if our proposed method can identify previously unseen malicious macros. Experimental results demonstrate that, compared to existing methods, our proposed method has a higher detection rate and better consistency. Furthermore, ensemble multi-classifiers with distinct feature selection can further enhance the detection performance.

Keywords

• malicious document
• VBA
• macro
• obfuscation
• suspicious keywords
• machine learning