Protocol Tunneling

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: Network Traffic: Network Connection Creation, Network Traffic: Network Traffic Content, Network Traffic: Network Traffic Flow
Version: 1.0
Created: 15 March 2020
Last Modified: 27 March 2020

Procedure Examples

ID Name Description
G0114 Chimera

Chimera has encapsulated Cobalt Strike's C2 protocol in DNS and HTTPS.[3]

G0080 Cobalt Group

Cobalt Group has used the Plink utility to create SSH tunnels.[4][5][6]

S0154 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.[7]

S0038 Duqu

Duqu uses a custom command and control protocol that communicates over commonly used ports, and is frequently encapsulated by application layer protocols.[8]

G0037 FIN6

FIN6 used the Plink command-line utility to create SSH tunnels to C2 servers.[9]

S0173 FLIPSIDE

FLIPSIDE uses RDP to tunnel traffic from a victim environment.[10]

G0117 Fox Kitten

Fox Kitten has used protocol tunneling for communication and RDP activity on compromised hosts through the use of open source tools such as Ngrok and custom tool SSHMinion.[11][12][13]

S0508 Ngrok

Ngrok can tunnel RDP and other services securely over internet connections.[14][15][16][17]

G0049 OilRig

OilRig has used the Plink utility and other tools to create tunnels to C2 servers.[18][19][20]

Mitigations

ID Mitigation Description
M1037 Filter Network Traffic

Consider filtering network traffic to untrusted or known bad domains and resources.

M1031 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.[21]

References