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Windows PowerShell Process Implementing Manual Base64 Decoder

The following analytic identifies Windows PowerShell processes that implement a manual Base64 decoder. Threat actors often use Base64 encoding to obfuscate malicious payloads or commands within PowerShell scripts. By…

Description

The following analytic identifies Windows PowerShell processes that implement a manual Base64 decoder. Threat actors often use Base64 encoding to obfuscate malicious payloads or commands within PowerShell scripts. By manually decoding Base64 strings, attackers can evade detection mechanisms that look for standard decoding functions like using the "-enc" flag or the "FromBase64String" function. This detection focuses on PowerShell processes that exhibit characteristics of manual Base64 decoding, such as the presence of specific string manipulation methods and bitwise operations. Security teams should investigate any instances of such activity, especially if found in conjunction with other suspicious behaviors or on systems that should not be using PowerShell for such tasks.

Detection logic

Detection requirements

Platform
LinuxmacOSWindows

The rule states no platform. This is derived from the 2 ATT&CK techniques it maps to.

Log source category
crowdstrike_processrollup2sysmon_eventid_1windows_event_log_security_4688

Known benign triggers

  • Legitimate use of PowerShell for decoding Base64 strings by administrators or power users may trigger this detection. It is essential to review the context of the PowerShell execution to determine if it is malicious, suspicious or even authorized activity.

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