Exfiltration Over Alternative Protocol

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Exfiltration Over Alternative Protocol
Technique
ID T1048
Tactic Exfiltration
Platform Windows Server 2003, Windows Server 2008, Windows Server 2012, Windows XP, Windows 7, Windows 8, Windows Server 2003 R2, Windows Server 2008 R2, Windows Server 2012 R2, Windows Vista, Windows 8.1, Linux, Windows 10, MacOS, OS X
Data Sources User interface, Process monitoring, Process use of network, Packet capture, Netflow/Enclave netflow, Network protocol analysis
Requires Network Yes

Data exfiltration is performed with a different protocol from the main command and control protocol or channel. The data is likely to be sent to an alternate network location from the main command and control server. Alternate protocols include FTP, SMTP, HTTP/S, DNS, or some other network protocol. Different channels could include Internet Web services such as cloud storage.

Examples

  • Lazarus Group malware SierraBravo-Two generates an email message via SMTP containing information about newly infected victims.1
  • Cherry Picker exfiltrates files over FTP.2
  • CosmicDuke exfiltrates collected files over FTP or WebDAV. Exfiltration servers can be separately configured from C2 servers.3
  • FTP may be used to exfiltrate data separate from the main command and control protocol.4
  • HAMMERTOSS exfiltrates data by uploading it to accounts created by the actors on Web cloud storage providers for the adversaries to retrieve later.5
  • Remsec can exfiltrate data via a DNS tunnel or email, separately from its C2 channel.6

Mitigation

Follow best practices for network firewall configurations to allow only necessary ports and traffic to enter and exit the network. For example, if services like FTP are not required for sending information outside of a network, then block FTP-related ports at the network perimeter. Enforce proxies and use dedicated servers for services such as DNS and only allow those systems to communicate over respective ports/protocols, instead of all systems within a network.7 These actions will help reduce command and control and exfiltration path opportunities.

Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary command and control infrastructure and malware can be used to mitigate activity at the network level. Signatures are often for unique indicators within protocols and may be based on the specific obfuscation technique used by a particular adversary or tool, and will likely be different across various malware families and versions. Adversaries will likely change tool command and control signatures over time or construct protocols in such a way to avoid detection by common defensive tools.8

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 communications that do not follow the expected protocol behavior for the port that is being used.8