Deobfuscate/Decode Files or Information
|Deobfuscate/Decode Files or Information|
|Data Sources||File monitoring, Process Monitoring, Process command-line parameters|
|Defense Bypassed||Anti-virus, Host intrusion prevention systems, Signature-based detection, Network intrusion detection system|
|Contributors||Matthew Demaske, Adaptforward|
Adversaries may use Obfuscated Files or Information to hide artifacts of an intrusion from analysis. They may require separate mechanisms to decode or deobfuscate that information depending on how they intend to use it. Methods for doing that include built-in functionality of malware, Scripting, PowerShell, or by using utilities present on the system.
- APT34 has used certutil to decode base64-encoded files on victims.2
- BRONZE BUTLER downloads encoded payloads and decodes them on the victim.3
- A OilRig macro has run a PowerShell command to decode file contents.4
- ISMInjector uses the
certutilcommand to decode a payload file.4
- Starloader decrypts and executes shellcode from a file called Stars.jps.5
- certutil has been used to decode binaries hidden inside certificate files as Base64 information.1
Identify unnecessary system utilities or potentially malicious software that may be used to deobfuscate or decode files or information, and audit and/or block them by using whitelisting6 tools, like AppLocker,78 or Software Restriction Policies9 where appropriate.10
Detecting the action of deobfuscating or decoding files or information may be difficult depending on the implementation. If the functionality is contained within malware and uses the Windows API, then attempting to detect malicious behavior before or after the action may yield better results than attempting to perform analysis on loaded libraries or API calls. If scripts are used, then collecting the scripts for analysis may be necessary. Perform process and command-line monitoring to detect potentially malicious behavior related to scripts and system utilities such as certutil.
- Malwarebytes Labs. (2017, March 27). New targeted attack against Saudi Arabia Government. Retrieved July 3, 2017.
- 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.
- Counter Threat Unit Research Team. (2017, October 12). BRONZE BUTLER Targets Japanese Enterprises. Retrieved January 4, 2018.
- Falcone, R. and Lee, B. (2017, October 9). OilRig Group Steps Up Attacks with New Delivery Documents and New Injector Trojan. Retrieved January 8, 2018.
- Symantec Security Response. (2017, November 7). Sowbug: Cyber espionage group targets South American and Southeast Asian governments. Retrieved November 16, 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.