|Platform||Linux, macOS, Windows|
|Data Sources||File monitoring, Binary file metadata, Process command-line parameters, Process monitoring|
An adversary may compress data (e.g., sensitive documents) that is collected prior to exfiltration in order to make it portable and minimize the amount of data sent over the network. The compression is done separately from the exfiltration channel and is performed using a custom program or algorithm, or a more common compression library or utility such as 7zip, RAR, ZIP, or zlib.
- APT1 has used RAR to compress files before moving them outside of the victim network.1
- APT3 has used tools to compress data before exfilling it. 2
- BRONZE BUTLER has compressed data into password-protected RAR archives prior to exfiltration.3
- CopyKittens uses ZPP, a .NET console program, to compress files with ZIP.4
- Following data collection, FIN6 has compressed log files into a ZIP archive prior to staging and exfiltration.5
- The Ke3chang group has been known to compress data before exfiltration.6
- Lazarus Group malware IndiaIndia saves information gathered about the victim to a file that is compressed with Zlib, encrypted, and uploaded to a C2 server.7 Lazarus Group malware RomeoDelta archives specified directories in .zip format, encrypts the .zip file, and uploads it to its C2 server.8
- Sowbug extracted documents and bundled them into a RAR archive.9
- Threat Group-3390 actors have compressed data into RAR files prior to exfiltration.10
- Threat Group-3390 has used RAR to compress, encrypt, and password-protect files prior to exfiltration.11
- menuPass has compressed files before exfiltration using TAR and RAR.1213
- ADVSTORESHELL compresses output data generated by command execution with a custom implementation of the Lempel–Ziv–Welch (LZW) algorithm.14
- Modules can be pushed to and executed by Duqu that copy data to a staging area, compress it, and XOR encrypt it.15
- Lurid can compress data before sending it.16
- After collecting documents from removable media, Prikormka compresses the collected files.17
- SeaDuke compressed data with zlib prior to sending it over C2.18
- The ZLib backdoor compresses communications using the standard Zlib compression library.19
Identify unnecessary system utilities, third-party tools, or potentially malicious software that may be used to compress files, and audit and/or block them by using whitelisting20 tools, like AppLocker,2122 or Software Restriction Policies23 where appropriate.24
If network intrusion prevention or data loss prevention tools are set to block specific file types from leaving the network over unencrypted channels, then an adversary may move to an encrypted channel.
Compression software and compressed files can be detected in many ways. Common utilities that may be present on the system or brought in by an adversary may be detectable through process monitoring and monitoring for command-line arguments for known compression utilities. This may yield a significant amount of benign events, depending on how systems in the environment are typically used.
If the communications channel is unencrypted, compressed files can be detected in transit during exfiltration with a network intrusion detection or data loss prevention system analyzing file headers.25
- Mandiant. (n.d.). APT1 Exposing One of China’s Cyber Espionage Units. Retrieved July 18, 2016.
- valsmith. (2012, September 21). More on APTSim. Retrieved September 28, 2017.
- Counter Threat Unit Research Team. (2017, October 12). BRONZE BUTLER Targets Japanese Enterprises. Retrieved January 4, 2018.
- ClearSky Cyber Security and Trend Micro. (2017, July). Operation Wilted Tulip: Exposing a cyber espionage apparatus. Retrieved August 21, 2017.
- FireEye Threat Intelligence. (2016, April). Follow the Money: Dissecting the Operations of the Cyber Crime Group FIN6. Retrieved June 1, 2016.
- Villeneuve, N., Bennett, J. T., Moran, N., Haq, T., Scott, M., & Geers, K. (2014). OPERATION “KE3CHANG”: Targeted Attacks Against Ministries of Foreign Affairs. Retrieved November 12, 2014.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Loaders, Installers and Uninstallers Report. Retrieved March 2, 2016.
- Novetta Threat Research Group. (2016, February 24). Operation Blockbuster: Remote Administration Tools & Content Staging Malware Report. Retrieved March 16, 2016.
- Symantec Security Response. (2017, November 7). Sowbug: Cyber espionage group targets South American and Southeast Asian governments. Retrieved November 16, 2017.
- Dell SecureWorks Counter Threat Unit Threat Intelligence. (2015, August 5). Threat Group-3390 Targets Organizations for Cyberespionage. Retrieved January 25, 2016.
- Counter Threat Unit Research Team. (2017, June 27). BRONZE UNION Cyberespionage Persists Despite Disclosures. Retrieved July 13, 2017.
- PwC and BAE Systems. (2017, April). Operation Cloud Hopper. Retrieved April 5, 2017.
- PwC and BAE Systems. (2017, April). Operation Cloud Hopper: Technical Annex. Retrieved April 13, 2017.
- ESET. (2016, October). En Route with Sednit - Part 2: Observing the Comings and Goings. Retrieved November 21, 2016.
- Symantec Security Response. (2011, November). W32.Duqu: The precursor to the next Stuxnet. Retrieved September 17, 2015.
- Villeneuve, N., Sancho, D. (2011). THE “LURID” DOWNLOADER. Retrieved November 12, 2014.
- Cherepanov, A.. (2016, May 17). Operation Groundbait: Analysis of a surveillance toolkit. Retrieved May 18, 2016.
- Dunwoody, M. and Carr, N.. (2016, September 27). No Easy Breach DerbyCon 2016. Retrieved October 4, 2016.
- Gross, J. (2016, February 23). Operation Dust Storm. Retrieved September 19, 2017.
- Beechey, J. (2010, December). Application Whitelisting: Panacea or Propaganda?. Retrieved November 18, 2014.
- Tomonaga, S. (2016, January 26). Windows Commands Abused by Attackers. Retrieved February 2, 2016.
- NSA Information Assurance Directorate. (2014, August). Application Whitelisting Using Microsoft AppLocker. Retrieved March 31, 2016.
- Corio, C., & Sayana, D. P. (2008, June). Application Lockdown with Software Restriction Policies. Retrieved November 18, 2014.
- Microsoft. (2012, June 27). Using Software Restriction Policies and AppLocker Policies. Retrieved April 7, 2016.
- Wikipedia. (2016, March 31). List of file signatures. Retrieved April 22, 2016.