File Decoded From Base64/Hex Via Certutil.EXE

testhigh
log source: windows · process_creationauthor Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.communitydate 2023-02-15
01

description

What this is, in brief.

Detects the execution of certutil with either the "decode" or "decodehex" flags to decode base64 or hex encoded files. This can be abused by attackers to decode an encoded payload before execution

02

tags

attack.stealthattack.t1027
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rule source (YAML)

title: File Decoded From Base64/Hex Via Certutil.EXE
id: cc9cbe82-7bc0-4ef5-bc23-bbfb83947be7
status: test
description: Detects the execution of certutil with either the "decode" or "decodehex" flags to decode base64 or hex encoded files. This can be abused by attackers to decode an encoded payload before execution
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://news.sophos.com/en-us/2021/04/13/compromised-exchange-server-hosting-cryptojacker-targeting-other-exchange-servers/
    - https://twitter.com/JohnLaTwC/status/835149808817991680
    - https://learn.microsoft.com/en-us/archive/blogs/pki/basic-crl-checking-with-certutil
    - https://lolbas-project.github.io/lolbas/Binaries/Certutil/
author: Florian Roth (Nextron Systems), Jonhnathan Ribeiro, oscd.community
date: 2023-02-15
modified: 2025-06-04
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:
            - '-decode ' # Decode Base64
            - '-decodehex ' # Decode Hex
    condition: all of selection_*
falsepositives:
    - Unknown
level: high
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_certutil_decode/info.yml
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detects techniques (1)

ATT&CK techniques this enables or maps to.

05

references

External citations — patches, advisories, analysis.