Execution Guardrails: Mutual Exclusion

Adversaries may constrain execution or actions based on the presence of a mutex associated with malware. A mutex is a locking mechanism used to synchronize access to a resource. Only one thread or process can acquire a mutex at a given time.^[1]

While local mutexes only exist within a given process, allowing multiple threads to synchronize access to a resource, system mutexes can be used to synchronize the activities of multiple processes.^[1] By creating a unique system mutex associated with a particular malware, adversaries can verify whether or not a system has already been compromised.^[2]

In Linux environments, malware may instead attempt to acquire a lock on a mutex file. If the malware is able to acquire the lock, it continues to execute; if it fails, it exits to avoid creating a second instance of itself.^[3][4]

Mutex names may be hard-coded or dynamically generated using a predictable algorithm.^[5]