Indicator Removal from Tools

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Indicator Removal from Tools
Technique
ID T1066
Tactic Defense Evasion
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, Linux, Windows 10, MacOS, OS X
Data Sources Process use of network, Anti-virus, Binary file metadata, Process command-line parameters, Process monitoring
Defense Bypassed Anti-virus, Log analysis, Host intrusion prevention systems

If a malicious tool is detected and quarantined or otherwise curtailed, an adversary may be able to determine why the malicious tool was detected (the indicator), modify the tool by removing the indicator, and use the updated version that is no longer detected by the target's defensive systems or subsequent targets that may use similar systems.

A good example of this is when malware is detected with a file signature and quarantined by anti-virus software. An adversary who can determine that the malware was quarantined because of its file signature may use Software Packing or otherwise modify the file so it has a different signature, and then re-use the malware.

Examples

  • Deep Panda has updated and modified its malware, resulting in different hash values that evade detection.1
  • OilRig has tested malware samples to determine AV detection and subsequently modified the samples to ensure AV evasion.2
  • Cobalt Strike includes a capability to modify the "beacon" payload to eliminate known signatures or unpacking methods.3

Mitigation

Mitigation is difficult in instances like this because the adversary may have access to the system through another channel and can learn what techniques or tools are blocked by resident defenses. Exercising best practices with configuration and security as well as ensuring that proper process is followed during investigation of potential compromise is essential to detecting a larger intrusion through discrete alerts.

Identify and block potentially malicious software that may be used by an adversary by using whitelisting4 tools like AppLocker56 or Software Restriction Policies7 where appropriate.8

Detection

The first detection of a malicious tool may trigger an anti-virus or other security tool alert. Similar events may also occur at the boundary through network IDS, email scanning appliance, etc. The initial detection should be treated as an indication of a potentially more invasive intrusion. The alerting system should be thoroughly investigated beyond that initial alert for activity that was not detected. Adversaries may continue with an operation, assuming that individual events like an anti-virus detect will not be investigated or that an analyst will not be able to conclusively link that event to other activity occurring on the network.