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.
|T1027.001, T1027.002, T1027.003, T1027.004, T1027.005, T1027.006, T1027.007, T1027.008, T1027.009, T1027.010, T1027.011
|Linux, Windows, macOS
|19 March 2020
|28 April 2022
|APT3 has been known to remove indicators of compromise from tools.
|Cobalt Strike includes a capability to modify the Beacon payload to eliminate known signatures or unpacking methods.
|Analysis of Daserf has shown that it regularly undergoes technical improvements to evade anti-virus detection.
|Deep Panda has updated and modified its malware, resulting in different hash values that evade detection.
|GALLIUM ensured each payload had a unique hash, including by using different types of packers.
|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.
|InvisiMole has undergone regular technical improvements in an attempt to evade detection.
|OilRig has tested malware samples to determine AV detection and subsequently modified the samples to ensure AV evasion.
|During Operation Wocao, threat actors edited variable names within the Impacket suite to avoid automated detection.
|Patchwork apparently altered NDiskMonitor samples by adding four bytes of random letters in a likely attempt to change the file hashes.
|Penquin can remove strings from binaries.
Find-AVSignature AntivirusBypass module can be used to locate single byte anti-virus signatures.
|QakBot can make small changes to itself in order to change its checksum and hash value.
|SUNBURST source code used generic variable names and pre-obfuscated strings, and was likely sanitized of developer comments before being added to SUNSPOT.
|TEMP.Veles has modified files based on the open-source project cryptcat in an apparent attempt to decrease AV detection rates.
|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.
|Waterbear can scramble functions not to be executed again with random values.