Base64 Encoding

SIGMA detection rule by RedCanary, Sigma formatting by Micah Babinski · GPL-3.0

If you’re looking to detect malicious use of Base64 encoding, consider monitoring for the execution of processes like powershell.exe or cmd.exe along with command lines containing parameters like ToBase64String and FromBase64String. The following simple pseudo-analytic might help you find malicious obfuscation. Part of the RedCanary 2024 Threat Detection Report.

title: Base64 Encoding
id: 027b8851-d448-4a3e-8f2e-698433ba81e3
status: experimental
description: |
    If you’re looking to detect malicious use of Base64 encoding, consider monitoring for the 
    execution of processes like powershell.exe or cmd.exe along with command lines containing 
    parameters like ToBase64String and FromBase64String. The following simple pseudo-analytic 
    might help you find malicious obfuscation. Part of the RedCanary 2024 Threat Detection 
    Report.
references:
    - https://redcanary.com/threat-detection-report/techniques/obfuscated-files-information/
author: RedCanary, Sigma formatting by Micah Babinski
date: 2024/03/21
tags:
    - attack.defense_evasion
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains: 'base64'
    condition: selection
falsepositives:
    - Unknown
level: low

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

370225c2-f612-47d3-898a-0a05e519253c

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

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