Data Compressed

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Data Compressed
Technique
ID T1002
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
Data Sources File monitoring, Binary file metadata, Process command-line parameters, Process monitoring
Requires Network No

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.

Examples

  • The Ke3chang group has been known to compress data before exfiltration.1
  • APT1 has used RAR to compress files before moving them outside of the victim network.2
  • Threat Group-3390 actors have compressed data into RAR files prior to exfiltration.3
  • 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.4 Lazarus Group malware RomeoDelta archives specified directories in .zip format, encrypts the .zip file, and uploads it to its C2 server.5
  • Following data collection, FIN6 has compressed log files into a ZIP archive prior to staging and exfiltration.6
  • Lurid can compress data before sending it.7
  • Modules can be pushed to and executed by Duqu that copy data to a staging area, compress it, and XOR encrypt it.8
  • ADVSTORESHELL compresses output data generated by command execution with a custom implementation of the Lempel–Ziv–Welch (LZW) algorithm.9
  • SeaDuke compressed data with zlib prior to sending it over C2.10
  • The ZLib backdoor compresses communications using the standard Zlib compression library.11
  • After collecting documents from removable media, Prikormka compresses the collected files.12

Mitigation

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 whitelisting13 tools, like AppLocker,1415 or Software Restriction Policies16 where appropriate.17

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.

Detection

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.18

References