The adversary is trying to communicate with compromised devices to control them.
The command and control tactic represents how adversaries communicate with systems under their control within a target network. There are many ways an adversary can establish command and control with various levels of covertness, depending on system configuration and network topology. Due to the wide degree of variation available to the adversary at the network level, only the most common factors were used to describe the differences in command and control. There are still a great many specific techniques within the documented methods, largely due to how easy it is to define new protocols and use existing, legitimate protocols and network services for communication.
The resulting breakdown should help convey the concept that detecting intrusion through command and control protocols without prior knowledge is a difficult proposition over the long term. Adversaries' main constraints in network-level defense avoidance are testing and deployment of tools to rapidly change their protocols, awareness of existing defensive technologies, and access to legitimate Web services that, when used appropriately, make their tools difficult to distinguish from benign traffic.
Additionally, in the mobile environment, mobile devices are frequently connected to networks outside enterprise control such as cellular networks or public Wi-Fi networks. Adversaries could attempt to evade detection by communicating on these networks, and potentially even by using non-Internet Protocol mechanisms such as Short Message Service (SMS). However, cellular networks often have data caps and/or extra data charges that could increase the potential for adversarial communication to be detected.
|T1438||Alternate Network Mediums||Adversaries can communicate using cellular networks rather than enterprise Wi-Fi in order to bypass enterprise network monitoring systems. Adversaries may also communicate using other non-Internet Protocol mediums such as SMS, NFC, or Bluetooth to bypass network monitoring systems.|
|T1616||Call Control||Adversaries may make, forward, or block phone calls without user authorization. This could be used for adversary goals such as audio surveillance, blocking or forwarding calls from the device owner, or C2 communication.|
|T1436||Commonly Used Port||Adversaries may communicate over a commonly used port to bypass firewalls or network detection systems and to blend with normal network activity to avoid more detailed inspection.|
|T1520||Domain Generation Algorithms||Adversaries may use Domain Generation Algorithms (DGAs) to procedurally generate domain names for command and control communication, and other uses such as malicious application distribution.|
|T1544||Remote File Copy||Files may be copied from one system to another to stage adversary tools or other files over the course of an operation. Files may be copied from an external adversary-controlled system through the Command and Control channel to bring tools into the victim network or onto the victim’s device.|
|T1437||Standard Application Layer Protocol||Adversaries may communicate using a common, standardized application layer protocol such as HTTP, HTTPS, SMTP, or DNS to avoid detection by blending in with existing traffic.|
|T1521||Standard Cryptographic Protocol||Adversaries may explicitly employ a known encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol. Despite the use of a secure algorithm, these implementations may be vulnerable to reverse engineering if necessary secret keys are encoded and/or generated within malware samples/configuration files.|
|T1509||Uncommonly Used Port||Adversaries may use non-standard ports to exfiltrate information.|
|T1481||Web Service||Adversaries may use an existing, legitimate external Web service as a means for relaying commands to a compromised system.|