Adversaries may tunnel network communications to and from a victim system within a separate protocol to avoid detection/network filtering and/or enable access to otherwise unreachable systems. Tunneling involves explicitly encapsulating a protocol within another. This behavior may conceal malicious traffic by blending in with existing traffic and/or provide an outer layer of encryption (similar to a VPN). Tunneling could also enable routing of network packets that would otherwise not reach their intended destination, such as SMB, RDP, or other traffic that would be filtered by network appliances or not routed over the Internet.

There are various means to encapsulate a protocol within another protocol. For example, adversaries may perform SSH tunneling (also known as SSH port forwarding), which involves forwarding arbitrary data over an encrypted SSH tunnel.^[1]

Protocol Tunneling may also be abused by adversaries during Dynamic Resolution. Known as DNS over HTTPS (DoH), queries to resolve C2 infrastructure may be encapsulated within encrypted HTTPS packets.^[2]

Adversaries may also leverage Protocol Tunneling in conjunction with Proxy and/or Protocol Impersonation to further conceal C2 communications and infrastructure.

ID: T1572

Sub-techniques: No sub-techniques

Tactic: Command And Control

Platforms: Linux, Windows, macOS

Data Sources: Netflow/Enclave netflow, Network protocol analysis, Packet capture, Process monitoring, Process use of network

Version: 1.0

Created: 15 March 2020

Last Modified: 27 March 2020

Version Permalink

Live Version

Procedure Examples

Name	Description
Cobalt Group	Cobalt Group has used the Plink utility to create SSH tunnels.^[7]^[8]^[9]
Cobalt Strike	Cobalt Strike uses a custom command and control protocol that is encapsulated in HTTP, HTTPS, or DNS. In addition, it conducts peer-to-peer communication over Windows named pipes encapsulated in the SMB protocol. All protocols use their standard assigned ports.^[3]
Duqu	Duqu uses a custom command and control protocol that communicates over commonly used ports, and is frequently encapsulated by application layer protocols.^[5]
FIN6	FIN6 used the Plink command-line utility to create SSH tunnels to C2 servers.^[6]
FLIPSIDE	FLIPSIDE uses RDP to tunnel traffic from a victim environment.^[4]
OilRig	OilRig has used the Plink utility and other tools to create tunnels to C2 servers.^[10]^[11]^[12]

Mitigations

Mitigation	Description
Filter Network Traffic	Consider filtering network traffic to untrusted or known bad domains and resources.
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.

Detection

Monitoring for systems listening and/or establishing external connections using ports/protocols commonly associated with tunneling, such as SSH (port 22). Also monitor for processes commonly associated with tunneling, such as Plink and the OpenSSH client.

Analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect application layer protocols that do not follow the expected protocol standards regarding syntax, structure, or any other variable adversaries could leverage to conceal data.^[13]

Protocol Tunneling

Procedure Examples

Mitigations

Detection

References