Application Layer Protocol: Mail Protocols

Adversaries may communicate using application layer protocols associated with electronic mail delivery to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.

Protocols such as SMTP/S, POP3/S, and IMAP that carry electronic mail may be very common in environments. Packets produced from these protocols may have many fields and headers in which data can be concealed. Data could also be concealed within the email messages themselves. An adversary may abuse these protocols to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.

ID: T1071.003
Sub-technique of:  T1071
Platforms: Linux, Windows, macOS
Data Sources: Network Traffic: Network Traffic Content, Network Traffic: Network Traffic Flow
Version: 1.0
Created: 15 March 2020
Last Modified: 21 October 2020

Procedure Examples

ID Name Description
S0331 Agent Tesla

Agent Tesla has used SMTP for C2 communications.[1][2][3]

G0007 APT28

APT28 used SMTP as a communication channel in various implants, initially using self-registered Google Mail accounts and later compromised email servers of its victims.[4]

G0050 APT32

APT32 has used email for C2 via an Office macro.[5][6]

S0337 BadPatch

BadPatch uses SMTP for C2.[7]

S0351 Cannon

Cannon uses SMTP/S and POP3/S for C2 communications by sending and receiving emails.[8]

S0023 CHOPSTICK

Various implementations of CHOPSTICK communicate with C2 over SMTP and POP3.[9]

S0126 ComRAT

ComRAT can use email attachments for command and control.[10]

S0137 CORESHELL

CORESHELL can communicate over SMTP and POP3 for C2.[4][11]

S0477 Goopy

Goopy has the ability to use a Microsoft Outlook backdoor macro to communicate with its C2.[6]

S0201 JPIN

JPIN can send email over SMTP.[12]

G0094 Kimsuky

Kimsuky has used e-mail to send exfiltrated data to C2 servers.[13]

S0395 LightNeuron

LightNeuron uses SMTP for C2.[14]

S0247 NavRAT

NavRAT uses the email platform, Naver, for C2 communications, leveraging SMTP.[15]

S0138 OLDBAIT

OLDBAIT can use SMTP for C2.[4]

S0495 RDAT

RDAT can use email attachments for C2 communications.[16]

S0125 Remsec

Remsec is capable of using SMTP for C2.[17][18][19]

G0083 SilverTerrier

SilverTerrier uses SMTP for C2 communications.[20]

G0010 Turla

Turla has used multiple backdoors which communicate with a C2 server via email attachments.[21]

S0251 Zebrocy

Zebrocy uses SMTP and POP3 for C2.[22][8][23][24][25][26]

Mitigations

ID Mitigation Description
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

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.[27]

References

  1. The DigiTrust Group. (2017, January 12). The Rise of Agent Tesla. Retrieved November 5, 2018.
  2. Zhang, X. (2017, June 28). In-Depth Analysis of A New Variant of .NET Malware AgentTesla. Retrieved November 5, 2018.
  3. Arsene, L. (2020, April 21). Oil & Gas Spearphishing Campaigns Drop Agent Tesla Spyware in Advance of Historic OPEC+ Deal. Retrieved May 19, 2020.
  4. FireEye. (2015). APT28: A WINDOW INTO RUSSIA’S CYBER ESPIONAGE OPERATIONS?. Retrieved August 19, 2015.
  5. Dahan, A. (2017, May 24). OPERATION COBALT KITTY: A LARGE-SCALE APT IN ASIA CARRIED OUT BY THE OCEANLOTUS GROUP. Retrieved November 5, 2018.
  6. Dahan, A. (2017). Operation Cobalt Kitty. Retrieved December 27, 2018.
  7. Bar, T., Conant, S. (2017, October 20). BadPatch. Retrieved November 13, 2018.
  8. Falcone, R., Lee, B. (2018, November 20). Sofacy Continues Global Attacks and Wheels Out New ‘Cannon’ Trojan. Retrieved November 26, 2018.
  9. ESET. (2016, October). En Route with Sednit - Part 2: Observing the Comings and Goings. Retrieved November 21, 2016.
  10. Faou, M. (2020, May). From Agent.btz to ComRAT v4: A ten-year journey. Retrieved June 15, 2020.
  11. Anthe, C. et al. (2015, October 19). Microsoft Security Intelligence Report Volume 19. Retrieved December 23, 2015.
  12. Windows Defender Advanced Threat Hunting Team. (2016, April 29). PLATINUM: Targeted attacks in South and Southeast Asia. Retrieved February 15, 2018.
  13. CISA, FBI, CNMF. (2020, October 27). https://us-cert.cisa.gov/ncas/alerts/aa20-301a. Retrieved November 4, 2020.
  14. Faou, M. (2019, May). Turla LightNeuron: One email away from remote code execution. Retrieved June 24, 2019.