Adversaries may use a connection proxy to direct network traffic between systems or act as an intermediary for network communications to a command and control server to avoid direct connections to their infrastructure. Many tools exist that enable traffic redirection through proxies or port redirection, including HTRAN, ZXProxy, and ZXPortMap.  Adversaries use these types of proxies 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.
External connection proxies are used to mask the destination of C2 traffic and are typically implemented with port redirectors. Compromised systems outside of the victim environment may be used for these purposes, as well as purchased infrastructure such as cloud-based resources or virtual private servers. Proxies may be chosen based on the low likelihood that a connection to them from a compromised system would be investigated. Victim systems would communicate directly with the external proxy on the internet and then the proxy would forward communications to the C2 server.
Internal connection proxies can be used to consolidate internal connections from compromised systems. Adversaries may use a compromised internal system as a proxy in order to conceal the true destination of C2 traffic. The proxy can redirect traffic from compromised systems inside the network to an external C2 server making discovery of malicious traffic difficult. Additionally, the network can be used to relay information from one system to another in order to avoid broadcasting traffic to all systems.
APT28 used other victims as proxies to relay command traffic, for instance using a compromised Georgian military email server as a hop point to NATO victims. The group has also used a tool that acts as a proxy to allow C2 even if the victim is behind a router. APT28 has also used a machine to relay and obscure communications between CHOPSTICK and their server.
Cobalt Strike can be configured to have commands relayed over a peer-to-peer network of infected hosts. This can be used to limit the number of egress points, or provide access to a host without direct internet access.
|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.
Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Network activities disassociated from user-driven actions from processes that normally require user direction are suspicious.
Analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server or between clients that should not or often do not communicate with one another). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect communications that do not follow the expected protocol behavior for the port that is being used. 
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