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Fallback Channels

Adversaries may use fallback or alternate communication channels if the primary channel is compromised or inaccessible in order to maintain reliable command and control and to avoid data transfer thresholds.

ID: T1008
Tactic: Command And Control
Platform: Linux, Windows, macOS
Data Sources: Malware reverse engineering, Netflow/Enclave netflow, Packet capture, Process monitoring, Process use of network
Requires Network:  Yes
Version: 1.0

Procedure Examples

Name Description
BISCUIT BISCUIT malware contains a secondary fallback command and control server that is contacted after the primary command and control server. [5] [6]
BlackEnergy BlackEnergy has the capability to communicate over a backup channel via plus.google.com. [8]
Cardinal RAT Cardinal RAT can communicate over multiple C2 host and port combinations. [10]
CHOPSTICK CHOPSTICK can switch to a new C2 channel if the current one is broken. [3]
Derusbi Derusbi uses a backup communication method with an HTTP beacon. [17]
DustySky DustySky has two hard-coded domains for C2 servers; if the first does not respond, it will try the second. [2]
HOPLIGHT HOPLIGHT has multiple C2 channels in place in case one fails. [18]
JHUHUGIT JHUHUGIT tests if it can reach its C2 server by first attempting a direct connection, and if it fails, obtaining proxy settings and sending the connection through a proxy, and finally injecting code into a running browser if the proxy method fails. [14]
Kazuar Kazuar can accept multiple URLs for C2 servers. [9]
Kwampirs Kwampirs uses a large list of C2 servers that it cycles through until a successful connection is established. [15]
Lazarus Group Lazarus Group malware SierraAlfa sends data to one of the hard-coded C2 servers chosen at random, and if the transmission fails, chooses a new C2 server to attempt the transmission again. [19] [20]
Linfo Linfo creates a backdoor through which remote attackers can change C2 servers. [7]
MiniDuke MiniDuke uses Google Search to identify C2 servers if its primary C2 method via Twitter is not working. [16]
Mis-Type Mis-Type first attempts to use a Base64-encoded network protocol over a raw TCP socket for C2, and if that method fails, falls back to a secondary HTTP-based protocol to communicate to an alternate C2 server. [4]
NETEAGLE NETEAGLE will attempt to detect if the infected host is configured to a proxy. If so, NETEAGLE will send beacons via an HTTP POST request; otherwise it will send beacons via UDP/6000. [13]
OilRig OilRig malware ISMAgent falls back to its DNS tunneling mechanism if it is unable to reach the C2 server over HTTP. [21]
QUADAGENT QUADAGENT uses multiple protocols (HTTPS, HTTP, DNS) for its C2 server as fallback channels if communication with one is unsuccessful. [11]
S-Type S-Type primarily uses port 80 for C2, but falls back to ports 443 or 8080 if initial communication fails. [4]
SslMM SslMM has a hard-coded primary and backup C2 string. [12]
WinMM WinMM is usually configured with primary and backup domains for C2 communications. [12]
XTunnel The C2 server used by XTunnel provides a port number to the victim to use as a fallback in case the connection closes on the currently used port. [3]

Mitigations

Mitigation Description
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. Signatures are often for unique indicators within protocols and may be based on the specific protocol 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. [1]

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. [1]

References