T1481Not expressible in SigmaMOBILE

Web Service

Command and ControlAndroid, iOS

Where this stands

No Sigma rule can address this — the telemetry MITRE names has no Sigma logsource behind it.

Sigma has no logsource taxonomy for mobile platforms. MITRE's telemetry here is mobile EDR and device APIs, which no Sigma rule can address.

What the technique is

Adversaries may use an existing, legitimate external Web service as a means for relaying data to/from a compromised system. Popular websites and social media, acting as a mechanism for C2, may give a significant amount of cover. This is 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, or enable operational resiliency (since this infrastructure may be dynamically changed).

Read it on attack.mitre.org

What MITRE says you would watch

AN1770
The defender correlates outbound communication from an application or service to legitimate external web platforms with mobile runtime context showing that the communication is inconsistent with the app's approved role, expected destinations, user interaction pattern, or device state. The strongest Android evidence is a managed or installed app communicating with cloud storage, social, messaging, code-hosting, or generic HTTPS web-service infrastructure shortly after background activation, protected-resource use, or local staging activity, especially when the device is locked, user interaction is absent, or the app's historical network baseline does not include that service class.
AN1771
The defender correlates communication to legitimate external web-service platforms with supervised managed-app context and device-state information showing that the traffic is inconsistent with the app's expected role, background-refresh profile, or user interaction timing. On iOS, the strongest reliable evidence is network telemetry tied to a managed app or device plus app state and supervision context, especially when traffic to social, collaboration, cloud-storage, or generic HTTPS platforms occurs shortly after background activity, while the device is locked, or without expected user-driven foreground execution. […]