Adversaries may remove indicators from tools if they believe their malicious tool was detected, quarantined, or otherwise curtailed. They can modify the tool by removing the indicator and using 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 modify the file to explicitly avoid that signature, and then re-use the malware.

ID: T1027.005

Sub-technique of: T1027

Tactic: Defense Evasion

Platforms: Linux, Windows, macOS

Data Sources: Anti-virus, Binary file metadata, Process command-line parameters, Process monitoring

Defense Bypassed: Anti-virus, Host intrusion prevention systems, Log analysis, Signature-based detection

Version: 1.0

Created: 19 March 2020

Last Modified: 29 March 2020

Version Permalink

Live Version

Procedure Examples

Name	Description
APT3	APT3 has been known to remove indicators of compromise from tools.^[11]
Cobalt Strike	Cobalt Strike includes a capability to modify the "beacon" payload to eliminate known signatures or unpacking methods.^[1]
Daserf	Analysis of Daserf has shown that it regularly undergoes technical improvements to evade anti-virus detection.^[5]
Deep Panda	Deep Panda has updated and modified its malware, resulting in different hash values that evade detection.^[6]
GravityRAT	The author of GravityRAT submitted samples to VirusTotal for testing, showing that the author modified the code to try to hide the DDE object in a different part of the document.^[4]
OilRig	OilRig has tested malware samples to determine AV detection and subsequently modified the samples to ensure AV evasion.^[8]^[9]
Patchwork	Patchwork apparently altered NDiskMonitor samples by adding four bytes of random letters in a likely attempt to change the file hashes.^[7]
PowerSploit	PowerSploit's `Find-AVSignature` AntivirusBypass module can be used to locate single byte anti-virus signatures.^[2]^[3]
Soft Cell	Soft Cell ensured each payload had a unique hash, including by using different types of packers.^[13]
TEMP.Veles	TEMP.Veles has modified files based on the open-source project cryptcat in an apparent attempt to decrease AV detection rates.^[12]
Turla	Based on comparison of Gazer versions, Turla made an effort to obfuscate strings in the malware that could be used as IoCs, including the mutex name and named pipe.^[10]

Mitigations

This type of attack technique cannot be easily mitigated with preventive controls since it is based on the abuse of system features.

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.

Obfuscated Files or Information: Indicator Removal from Tools

Other sub-techniques of Obfuscated Files or Information (5)

Procedure Examples

Mitigations

Detection

References