Standard Non-Application Layer Protocol

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Standard Non-Application Layer Protocol
Technique
ID T1095
Tactic Command and Control
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
Requires Network Yes

Use of a standard non-application layer protocol for communication between host and C2 server or among infected hosts within a network. The list of possible protocols is extensive.1 Specific examples include use of network layer protocols, such as the Internet Control Message Protocol (ICMP), and transport layer protocols, such as the User Datagram Protocol (UDP).

ICMP communication between hosts is one example. Because ICMP is part of the Internet Protocol Suite, it is required to be implemented by all IP-compatible hosts;2 however, it is not as commonly monitored as other Internet Protocols such as TCP or UDP and may be used by adversaries to hide communications.

Examples

  • An APT3 downloader establishes SOCKS5 connections for its initial C2.3
  • PlugX can be configured to use raw TCP or UDP for command and control.4
  • The Regin malware platform can use ICMP to communicate between infected computers.5
  • Derusbi binds to a raw socket on a random source port between 31800 and 31900 for C2.6
  • If NETEAGLE does not detect a proxy configured on the infected machine, it will send beacons via UDP/6000. Also, after retrieving a C2 IP address and Port Number, NETEAGLE will initiate a TCP connection to this socket. The ensuing connection is a plaintext C2 channel in which commands are specified by DWORDs.7
  • BUBBLEWRAP can communicate using SOCKS.8
  • Misdat network traffic communicates over a raw socket.9
  • Mis-Type network traffic can communicate over a raw socket.9
  • Crimson uses a custom TCP protocol for C2.10
  • Remsec is capable of using ICMP, TCP, and UDP for C2.1112

Mitigation

Properly configure firewalls and proxies to limit outgoing traffic to only necessary ports and through proper network gateway systems.

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. 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 C2 signatures over time or construct protocols in such a way as to avoid detection by common defensive tools.13

Detection

Analyze network traffic for ICMP messages or other protocols that contain abnormal data or are not normally seen within or exiting the network.

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.13

References