File Encoded To Base64 Via Certutil.EXE

Detects the execution of certutil with the "encode" flag to encode a file to base64. This can be abused by threat actors and attackers for data exfiltration

title: File Encoded To Base64 Via Certutil.EXE
id: e62a9f0c-ca1e-46b2-85d5-a6da77f86d1a
status: test
description: Detects the execution of certutil with the "encode" flag to encode a file to base64. This can be abused by threat actors and attackers for data exfiltration
references:
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
    - https://unit42.paloaltonetworks.com/new-babyshark-malware-targets-u-s-national-security-think-tanks/
    - https://lolbas-project.github.io/lolbas/Binaries/Certutil/
author: Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community, Nasreddine Bencherchali (Nextron Systems)
date: 2019-02-24
modified: 2024-03-05
tags:
    - attack.stealth
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\certutil.exe'
        - OriginalFileName: 'CertUtil.exe'
    selection_cli:
        CommandLine|contains|windash: '-encode'
    condition: all of selection_*
falsepositives:
    - As this is a general purpose rule, legitimate usage of the encode functionality will trigger some false positives. Apply additional filters accordingly
level: medium
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_certutil_encode/info.yml

• T1027Obfuscated Files or Information

• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/certutil↗
• https://unit42.paloaltonetworks.com/new-babyshark-malware-targets-u-s-national-security-think-tanks/↗
• https://lolbas-project.github.io/lolbas/Binaries/Certutil/↗