One of the most difficult objectives to obtain in the analysis of a malicious binary is usually discovering all of the functionalities that it has. If in addition, these functions are only executed at the discretion of the attackers through its control center, things get complicated. For various reasons, many times we cannot carry out a full dynamic analysis, such as the fall of the malware infrastructure or the isolation of the sample to avoid contact with the C&C. In these cases the analysis of the interaction between the server of the attacker and the sample is usually slower, since you have to create a fictitious server or be continually patching/deceiving the sample, to take it through all the different paths that we want to investigate. Depending on the size and complexity of the analyzed code or the objective of the analysis, this task can vary its difficulty and extension over time.
I am going to propose a study example of the functionalities of a fictitious RAT that can be executed according to the orders received from your C&C panel. Our goal would be to create a server that simulates the attacker’s. For this we have to understand the communication protocol between the server and the sample installed on the victim’s device.
