|Tactic||Command and Control|
|Platform||Linux, macOS, Windows|
|Data Sources||Packet capture, Process use of network, Process monitoring, Network protocol analysis|
Command and control (C2) communications are hidden (but not necessarily encrypted) in an attempt to make the content more difficult to discover or decipher and to make the communication less conspicuous and hide commands from being seen. This encompasses many methods, such as adding junk data to protocol traffic, using steganography, commingling legitimate traffic with C2 communications traffic, or using a non-standard data encoding system, such as a modified Base64 encoding for the message body of an HTTP request.
- APT28 added "junk data" to each encoded string, preventing trivial decoding without knowledge of the junk removal algorithm. Each implant was given a "junk length" value when created, tracked by the controller software to allow seamless communication but prevent analysis of the command protocol on the wire.1
- The Axiom group has used other forms of obfuscation, include commingling legitimate traffic with communications traffic so that network streams appear legitimate. Some malware that has been used by Axiom also uses steganography to hide communication in PNG image files.2
- Newer variants of BACKSPACE will encode C2 communications with a custom system.3
- After encrypting C2 data, BADNEWS converts it into a hexadecimal representation and then encodes it into base64.4
- Some Backdoor.Oldrea samples use standard Base64 + bzip2, and some use standard Base64 + reverse XOR + RSA-2048 to decrypt data received from C2 servers.5
- Daserf can use steganography to hide malicious code downloaded to the victim.6
- Downdelph inserts pseudo-random characters between each original character during encoding of C2 network requests, making it difficult to write signatures on them.7
- When the Duqu command and control is operating over HTTP or HTTPS, Duqu uploads data to its controller by appending it to a blank JPG file.8
- FakeM C2 traffic attempts to evade detection by resembling data generated by legitimate messenger applications, such as MSN and Yahoo! messengers.9
- H1N1 obfuscates C2 traffic with an altered version of base64.10
- HAMMERTOSS is controlled via commands that are appended to image files.11
- The Ixeshe malware uses custom Base64 encoding schemes to obfuscate data command and control traffic in the message body of HTTP requests.12
- P2P ZeuS added junk data to outgoing UDP packets to peer implants.13
- POWERSTATS encoded C2 traffic with base64.14
- POWRUNER can use base64 encoded C2 communications.15
- ZeroT has retrieved stage 2 payloads as Bitmap images that use Least Significant Bit (LSB) steganography.1617
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.18
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.18
- FireEye. (2015). APT28: A WINDOW INTO RUSSIA’S CYBER ESPIONAGE OPERATIONS?. Retrieved August 19, 2015.
- Novetta. (n.d.). Operation SMN: Axiom Threat Actor Group Report. Retrieved November 12, 2014.
- FireEye Labs. (2015, April). APT30 AND THE MECHANICS OF A LONG-RUNNING CYBER ESPIONAGE OPERATION. Retrieved May 1, 2015.
- Settle, A., et al. (2016, August 8). MONSOON - Analysis Of An APT Campaign. Retrieved September 22, 2016.
- Symantec Security Response. (2014, July 7). Dragonfly: Cyberespionage Attacks Against Energy Suppliers. Retrieved April 8, 2016.
- Chen, J. and Hsieh, M. (2017, November 7). REDBALDKNIGHT/BRONZE BUTLER’s Daserf Backdoor Now Using Steganography. Retrieved December 27, 2017.
- ESET. (2016, October). En Route with Sednit - Part 3: A Mysterious Downloader. Retrieved November 21, 2016.
- Symantec Security Response. (2011, November). W32.Duqu: The precursor to the next Stuxnet. Retrieved September 17, 2015.
- Falcone, R. and Miller-Osborn, J.. (2016, January 24). Scarlet Mimic: Years-Long Espionage Campaign Targets Minority Activists. Retrieved February 10, 2016.
- Reynolds, J.. (2016, September 14). H1N1: Technical analysis reveals new capabilities – part 2. Retrieved September 26, 2016.
- FireEye Labs. (2015, July). HAMMERTOSS: Stealthy Tactics Define a Russian Cyber Threat Group. Retrieved September 17, 2015.
- Moran, N., & Villeneuve, N. (2013, August 12). Survival of the Fittest: New York Times Attackers Evolve Quickly [Blog]. Retrieved November 12, 2014.
- SecureWorks. (2013). The Lifecycle of Peer-to-Peer (Gameover) ZeuS. Retrieved August 19, 2015.
- Lancaster, T.. (2017, November 14). Muddying the Water: Targeted Attacks in the Middle East. Retrieved March 15, 2018.
- Sardiwal, M, et al. (2017, December 7). New Targeted Attack in the Middle East by APT34, a Suspected Iranian Threat Group, Using CVE-2017-11882 Exploit. Retrieved December 20, 2017.
- Axel F. (2017, April 27). APT Targets Financial Analysts with CVE-2017-0199. Retrieved February 15, 2018.
- Huss, D., et al. (2017, February 2). Oops, they did it again: APT Targets Russia and Belarus with ZeroT and PlugX. Retrieved April 5, 2018.
- Gardiner, J., Cova, M., Nagaraja, S. (2014, February). Command & Control Understanding, Denying and Detecting. Retrieved April 20, 2016.