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.
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.
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.
|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.
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.
- SSH.COM. (n.d.). SSH tunnel. Retrieved March 15, 2020.
- Gatlan, S. (2019, July 3). New Godlua Malware Evades Traffic Monitoring via DNS over HTTPS. Retrieved March 15, 2020.
- Svajcer, V. (2018, July 31). Multiple Cobalt Personality Disorder. Retrieved September 5, 2018.
- Positive Technologies. (2016, December 16). Cobalt Snatch. Retrieved October 9, 2018.
- Matveeva, V. (2017, August 15). Secrets of Cobalt. Retrieved October 10, 2018.
- Strategic Cyber LLC. (2017, March 14). Cobalt Strike Manual. Retrieved May 24, 2017.
- Symantec Security Response. (2011, November). W32.Duqu: The precursor to the next Stuxnet. Retrieved September 17, 2015.
- FireEye Threat Intelligence. (2016, April). Follow the Money: Dissecting the Operations of the Cyber Crime Group FIN6. Retrieved June 1, 2016.
- Bromiley, M. and Lewis, P. (2016, October 7). Attacking the Hospitality and Gaming Industries: Tracking an Attacker Around the World in 7 Years. Retrieved October 6, 2017.
- Kennelly, J., Goody, K., Shilko, J. (2020, May 7). Navigating the MAZE: Tactics, Techniques and Procedures Associated With MAZE Ransomware Incidents. Retrieved May 18, 2020.
- Cyware. (2019, May 29). Cyber attackers leverage tunneling service to drop Lokibot onto victims’ systems. Retrieved September 15, 2020.
- Segura, J. (2020, February 26). Fraudsters cloak credit card skimmer with fake content delivery network, ngrok server. Retrieved September 15, 2020.
- Borja, A. Camba, A. et al (2020, September 14). Analysis of a Convoluted Attack Chain Involving Ngrok. Retrieved September 15, 2020.
- Unit 42. (2017, December 15). Unit 42 Playbook Viewer. Retrieved December 20, 2017.
- Davis, S. and Caban, D. (2017, December 19). APT34 - New Targeted Attack in the Middle East. Retrieved December 20, 2017.
- Bromiley, M., et al.. (2019, July 18). Hard Pass: Declining APT34’s Invite to Join Their Professional Network. Retrieved August 26, 2019.
- Gardiner, J., Cova, M., Nagaraja, S. (2014, February). Command & Control Understanding, Denying and Detecting. Retrieved April 20, 2016.