|Platform||Linux, macOS, Windows|
|Defense Bypassed||Anti-virus, Signature-based detection|
Some security tools inspect files with static signatures to determine if they are known malicious. Adversaries may add data to files to increase the size beyond what security tools are capable of handling or to change the file hash to avoid hash-based blacklists.
- BRONZE BUTLER downloader code has included "0" characters at the end of the file to inflate the file size in a likely attempt to evade anti-virus detection.1
- Moafee has been known to employ binary padding.2
- CORESHELL contains unused machine instructions in a likely attempt to hinder analysis.3
- A variant of Emissary appends junk data to the end of its DLL file to create a large file that may exceed the maximum size that anti-virus programs can scan.4
- A version of XTunnel introduced in July 2015 inserted junk code into the binary in a likely attempt to obfuscate it and bypass security products.5
Identify potentially malicious software that may be executed from a padded or otherwise obfuscated binary, and audit and/or block it by using whitelisting6 tools, like AppLocker,78 or Software Restriction Policies9 where appropriate.10
Depending on the method used to pad files, a file-based signature may be capable of detecting padding using a scanning or on-access based tool.
When executed, the resulting process from padded files may also exhibit other behavior characteristics of being used to conduct an intrusion such as system and network information Discovery or Lateral Movement, which could be used as event indicators that point to the source file.
- Counter Threat Unit Research Team. (2017, October 12). BRONZE BUTLER Targets Japanese Enterprises. Retrieved January 4, 2018.
- Haq, T., Moran, N., Scott, M., & Vashisht, S. O. (2014, September 10). The Path to Mass-Producing Cyber Attacks [Blog]. Retrieved November 12, 2014.
- FireEye. (2015). APT28: A WINDOW INTO RUSSIA’S CYBER ESPIONAGE OPERATIONS?. Retrieved August 19, 2015.
- Falcone, R. and Miller-Osborn, J.. (2016, February 3). Emissary Trojan Changelog: Did Operation Lotus Blossom Cause It to Evolve?. Retrieved February 15, 2016.
- ESET. (2016, October). En Route with Sednit - Part 2: Observing the Comings and Goings. Retrieved November 21, 2016.
- 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.