T1071.003sub-technique of T1071 Application Layer Protocol
Mail Protocols
Linux · macOS · Network Devices · Windowsnothing on this site yetT1071.003 on attack.mitre.org
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.
how MITRE says to see it
Detection of Mail Protocol-Based C2 Activity (SMTP, IMAP, POP3)
- Detects unauthorized use of SMTP/IMAP/POP3 by suspicious binaries (e.g., PowerShell, rundll32) to exfiltrate data or beacon via email, often bypassing proxy or content filters.
- Detects non-interactive or script-driven email transmission using tools like `sendmail`, `mailx`, or custom SMTP scripts by background processes, especially when sending attachments or large payloads.
- Detects email-sending behavior via Terminal, AppleScript, or Automator that interfaces with SMTP or IMAP, typically using curl or mail-related APIs in unsanctioned contexts.
- Detects hosts transmitting large volumes of SMTP, IMAP, or POP3 traffic to external IPs or relays that aren't associated with the enterprise mail infrastructure.
what reduces it
- 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.
- M1037 Filter Network Traffic. Limit the ability of servers and critical systems to initiate outbound email communications. Filtering SMTP/IMAP/POP3 traffic to only trusted mail servers reduces the risk of attackers using compromised systems to exfiltrate data via email or to receive commands from attacker-controlled email accounts.