Adversaries may use an existing, legitimate external Web service as a means for relaying commands to a compromised system.
These commands may also include pointers to command and control (C2) infrastructure. Adversaries may post content, known as a dead drop resolver, on Web services with embedded (and often obfuscated/encoded) domains or IP addresses. Once infected, victims will reach out to and be redirected by these resolvers.
Popular websites and social media acting as a mechanism for C2 may give a significant amount of cover due to the likelihood that hosts within a network are already communicating with them prior to a compromise. Using common services, such as those offered by Google or Twitter, makes it easier for adversaries to hide in expected noise. Web service providers commonly use SSL/TLS encryption, giving adversaries an added level of protection.
Use of Web services may also protect back-end C2 infrastructure from discovery through malware binary analysis while also enabling operational resiliency (since this infrastructure may be dynamically changed).
ANDROIDOS_ANSERVER.A uses encrypted content within a blog site for part of its command and control. Specifically, the encrypted content contains URLs for other servers to be used for other aspects of command and control.
This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.