Web Service: One-Way Communication

Adversaries may use an existing, legitimate external Web service as a means for sending commands to a compromised system without receiving return output over the Web service channel. Compromised systems may leverage popular websites and social media to host command and control (C2) instructions. Those infected systems may opt to send the output from those commands back over a different C2 channel, including to another distinct Web service. Alternatively, compromised systems may return no output at all in cases where adversaries want to send instructions to systems and do not want a response.

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.

ID: T1102.003
Sub-technique of:  T1102
Tactic: Command And Control
Platforms: Linux, Windows, macOS
Permissions Required: User
Data Sources: Host network interface, Netflow/Enclave netflow, Network protocol analysis, Packet capture, SSL/TLS inspection
Version: 1.0
Created: 14 March 2020
Last Modified: 26 March 2020

Procedure Examples

Name Description
HAMMERTOSS

The "tDiscoverer" variant of HAMMERTOSS establishes a C2 channel by downloading resources from Web services like Twitter and GitHub. HAMMERTOSS binaries contain an algorithm that generates a different Twitter handle for the malware to check for instructions every day.[1]

Leviathan

Leviathan has received C2 instructions from user profiles created on legitimate websites such as Github and TechNet.[2]

Metamorfo

Metamorfo has downloaded a zip file for execution on the system.[3][4][5]

OnionDuke

OnionDuke uses Twitter as a backup C2.[6]

Mitigations

Mitigation Description
Network Intrusion Prevention

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level.

Restrict Web-Based Content

Web proxies can be used to enforce external network communication policy that prevents use of unauthorized external services.

Detection

Host data that can relate unknown or suspicious process activity using a network connection is important to supplement any existing indicators of compromise based on malware command and control signatures and infrastructure or the presence of strong encryption. Packet capture analysis will require SSL/TLS inspection if data is encrypted. Analyze network data for uncommon data flows. User behavior monitoring may help to detect abnormal patterns of activity.[7]

References