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]

References

  1. Microsoft. (2022, March 11). Mutexes. Retrieved September 19, 2024.
  2. Lenny Zeltser. (2012, July 24). Looking at Mutex Objects for Malware Discovery & Indicators of Compromise. Retrieved September 19, 2024.
  3. Joakim Kennedy and Avigayil Mechtinger. (2021, March 10). New Linux Backdoor RedXOR Likely Operated by Chinese Nation-State Actor. Retrieved September 19, 2024.
  4. Shaul Vilkomir-Preisman and Eliran Nissan. (2023, May 10). BPFDoor Malware Evolves – Stealthy Sniffing Backdoor Ups Its Game. Retrieved September 19, 2024.
  5. Lenny Zeltser. (2015, March 9). How Malware Generates Mutex Names to Evade Detection. Retrieved September 19, 2024.

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