| ID | Name |
|---|---|
| T1090.001 | Internal Proxy |
| T1090.002 | External Proxy |
| T1090.003 | Multi-hop Proxy |
| T1090.004 | Domain Fronting |
To disguise the source of malicious traffic, adversaries may chain together multiple proxies. Typically, a defender will be able to identify the last proxy traffic traversed before it enters their network; the defender may or may not be able to identify any previous proxies before the last-hop proxy. This technique makes identifying the original source of the malicious traffic even more difficult by requiring the defender to trace malicious traffic through several proxies to identify its source. A particular variant of this behavior is to use onion routing networks, such as the publicly available TOR network. [1]
In the case of network infrastructure, particularly routers, it is possible for an adversary to leverage multiple compromised devices to create a multi-hop proxy chain within the Wide-Area Network (WAN) of the enterprise. By leveraging Patch System Image, adversaries can add custom code to the affected network devices that will implement onion routing between those nodes. This custom onion routing network will transport the encrypted C2 traffic through the compromised population, allowing adversaries to communicate with any device within the onion routing network. This method is dependent upon the Network Boundary Bridging method in order to allow the adversaries to cross the protected network boundary of the Internet perimeter and into the organization’s WAN. Protocols such as ICMP may be used as a transport.
| ID | Name | Description |
|---|---|---|
| G0007 | APT28 |
APT28 has routed traffic over Tor and VPN servers to obfuscate their activities.[2] |
| G0016 | APT29 |
A backdoor used by APT29 created a Tor hidden service to forward traffic from the Tor client to local ports 3389 (RDP), 139 (Netbios), and 445 (SMB) enabling full remote access from outside the network and has also used TOR.[3][4] |
| S0438 | Attor | |
| G0132 | CostaRicto |
CostaRicto has used a layer of proxies to manage C2 communications.[6] |
| S0687 | Cyclops Blink |
Cyclops Blink has used Tor nodes for C2 traffic.[7] |
| S0281 | Dok | |
| S0384 | Dridex |
Dridex can use multiple layers of proxy servers to hide terminal nodes in its infrastructure.[9] |
| G0085 | FIN4 | |
| S0342 | GreyEnergy |
GreyEnergy has used Tor relays for Command and Control servers.[11] |
| G0100 | Inception |
Inception used chains of compromised routers to proxy C2 communications between them and cloud service providers.[12] |
| S0604 | Industroyer |
Industroyer used Tor nodes for C2.[13] |
| S0276 | Keydnap |
Keydnap uses a copy of tor2web proxy for HTTPS communications.[14] |
| S0641 | Kobalos |
Kobalos can chain together multiple compromised machines as proxies to reach their final targets.[15][16] |
| G0065 | Leviathan |
Leviathan has used multi-hop proxies to disguise the source of their malicious traffic.[17] |
| S0282 | MacSpy | |
| G0116 | Operation Wocao |
Operation Wocao has executed commands through the installed web shell via Tor exit nodes.[18] |
| S0623 | Siloscape | |
| S0491 | StrongPity |
StrongPity can use multiple layers of proxy servers to hide terminal nodes in its infrastructure.[20] |
| S0183 | Tor |
Traffic traversing the Tor network will be forwarded to multiple nodes before exiting the Tor network and continuing on to its intended destination.[21] |
| S0386 | Ursnif | |
| S0366 | WannaCry |
| ID | Mitigation | Description |
|---|---|---|
| M1037 | 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. |
| ID | Data Source | Data Component |
|---|---|---|
| DS0029 | Network Traffic | Network Connection Creation |
| Network Traffic Content | ||
| Network Traffic Flow |
When observing use of Multi-hop proxies, network data from the actual command and control servers could allow correlating incoming and outgoing flows to trace malicious traffic back to its source. Multi-hop proxies can also be detected by alerting on traffic to known anonymity networks (such as Tor) or known adversary infrastructure that uses this technique.
In context of network devices, monitor traffic for encrypted communications from the Internet that is addressed to border routers. Compare this traffic with the configuration to determine whether it matches with any configured site-to-site Virtual Private Network (VPN) connections the device was intended to have. Monitor traffic for encrypted communications originating from potentially breached routers that is addressed to other routers within the organization. Compare the source and destination with the configuration of the device to determine if these channels are an authorized Virtual Private Network (VPN) connections or other encrypted modes of communication. Monitor ICMP traffic from the Internet that is addressed to border routers and is encrypted. Few if any legitimate use cases exist for sending encrypted data to a network device via ICMP.