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Connection Proxy

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Connection Proxy
Technique
ID T0884
Tactic Command and Control
Data Sources Network Traffic: Network Connection Creation, Network Traffic: Network Traffic Content, Network Traffic: Network Traffic Flow

Description

Adversaries may use a connection proxy to direct network traffic between systems or act as an intermediary for network communications.

The definition of a proxy can also be expanded to encompass trust relationships between networks in peer-to-peer, mesh, or trusted connections between networks consisting of hosts or systems that regularly communicate with each other.

The network may be within a single organization or across multiple organizations with trust relationships. Adversaries could use these types of relationships to manage command and control communications, to reduce the number of simultaneous outbound network connections, to provide resiliency in the face of connection loss, or to ride over existing trusted communications paths between victims to avoid suspicion.1


Procedure Examples

  • Sandworm Team establishes an internal proxy prior to the installation of backdoors within the network.2
  • Industroyer attempts to connect with a hardcoded internal proxy on TCP 3128 [default Squid proxy]. If established, the backdoor attempts to reach an external C2 server via the internal proxy.2

Mitigations

  • Network Allowlists - Network allowlists can be implemented through either host-based files or system host files to specify what external connections (e.g., IP address, MAC address, port, protocol) can be made from a device. Allowlist techniques that operate at the application layer (e.g., DNP3, Modbus, HTTP) are addressed in the Filter Network Traffic mitigation.
  • 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. Signatures are often for unique indicators within protocols and may be based on the specific C2 protocol used by a particular adversary or tool and will likely be different across various malware families and versions. Adversaries will likely change tool C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.3
  • Filter Network Traffic - Traffic to known anonymity networks and C2 infrastructure can be blocked through the use of network allow and block lists. It should be noted that this kind of blocking may be circumvented by other techniques like Domain Fronting.
  • SSL/TLS Inspection - If it is possible to inspect HTTPS traffic, the captures can be analyzed for connections that appear to be domain fronting.