Binary Padding

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Binary Padding
ID T1009
Tactic Defense Evasion
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
  • Leviathan has inserted garbage characters into code, presumably to avoid anti-virus detection.2
  • Moafee has been known to employ binary padding.3
  • CORESHELL contains unused machine instructions in a likely attempt to hinder analysis.4
  • 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.5
  • 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.6
  • ZeroT has obfuscated DLLs and functions using dummy API calls inserted between real instructions.7


Identify potentially malicious software that may be executed from a padded or otherwise obfuscated binary, and audit and/or block it by using whitelisting8 tools, like AppLocker,910 or Software Restriction Policies11 where appropriate.12


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.