A connection proxy is used to direct network traffic between systems or act as an intermediary for network communications. Many tools exist that enable traffic redirection through proxies or port redirection, including HTRAN, ZXProxy, and ZXPortMap. 
The definition of a proxy can also be expanded out 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 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.
|APT28||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.   |
|APT3||An APT3 downloader establishes SOCKS5 connections for its initial C2. |
|APT39||APT39 used custom tools to create SOCK5 proxies between infected hosts. |
|AuditCred||AuditCred can utilize proxy for communications. |
|BACKSPACE||The "ZJ" variant of BACKSPACE allows "ZJ link" infections with Internet access to relay traffic from "ZJ listen" to a command server. |
|BADCALL||BADCALL functions as a proxy server between the victim and C2 server. |
|Cardinal RAT||Cardinal RAT can act as a reverse proxy. |
|CHOPSTICK||CHOPSTICK used a proxy server between victims and the C2 server. |
|Cobalt Strike||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. |
|Dridex||Dridex contains a backconnect module for tunneling network traffic through a victim's computer. Infected computers become part of a P2P botnet that can relay C2 traffic to other infected peers. |
|Duqu||Duqu can be configured to have commands relayed over a peer-to-peer network of infected hosts if some of the hosts do not have Internet access. |
|FLIPSIDE||FLIPSIDE is a simple proxy that creates an outbound RDP connection. |
|Gazer||Gazer identifies a proxy server if it exists and uses it to make HTTP requests. |
HARDRAIN uses the command
|Hikit||Hikit supports peer connections. |
|HOPLIGHT||HOPLIGHT has multiple proxy options that mask traffic between the malware and the remote operators. |
|HTRAN||HTRAN can proxy TCP socket connections to obfuscate command and control infrastructure.  |
|InvisiMole||InvisiMole can function as a proxy to create a serve that relays communication between the client and C&C server. |
|jRAT||jRAT can serve as a SOCKS proxy server. |
|Lazarus Group||Lazarus Group uses multiple proxies to obfuscate network traffic from victims. |
|menuPass||menuPass has used a global service provider's IP as a proxy for C2 traffic from a victim.  |
|MuddyWater||MuddyWater has controlled POWERSTATS from behind a proxy network to obfuscate the C2 location. |
|netsh||netsh can be used to set up a proxy tunnel to allow remote host access to an infected host. |
|PoshC2||PoshC2 contains modules that allow for use of proxies in command and control. |
|POWERSTATS||POWERSTATS has connected to C2 servers through proxies. |
|QuasarRAT||QuasarRAT can communicate over a reverse proxy using SOCKS5.  |
|Regin||Regin leveraged several compromised universities as proxies to obscure its origin. |
|Remcos||Remcos uses the infected hosts as SOCKS5 proxies to allow for tunneling and proxying. |
|Socksbot||Socksbot can start SOCKS proxy threads. |
|Soft Cell||Soft Cell used a modified version of HTRAN to redirect connections between networks. |
|Strider||Strider has used local servers with both local network and Internet access to act as internal proxy nodes to exfiltrate data from other parts of the network without direct Internet access. |
|Turla||Turla RPC backdoors have included local UPnP RPC proxies. |
|TYPEFRAME||A TYPEFRAME variant can force the compromised system to function as a proxy server. |
|Ursnif||Ursnif has used a peer-to-peer (P2P) network for C2.  |
|Vasport||Vasport is capable of tunneling though a proxy. |
|XTunnel||XTunnel relays traffic between a C2 server and a victim. |
|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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