Suspicious Certutil Command Usage

SIGMA detection rule by Florian Roth (Nextron Systems), juju4, keepwatch · GPL-2.0

Detects a suspicious Microsoft certutil execution with sub commands like 'decode' sub command, which is sometimes used to decode malicious code

title: Suspicious Certutil Command Usage
id: 540f0d7f-8d92-2c4b-ce07-2be23d582ede
related:
    - id: e011a729-98a6-4139-b5c4-bf6f6dd8239a
      type: derived
status: deprecated
description: Detects a suspicious Microsoft certutil execution with sub commands like 'decode' sub command, which is sometimes used to decode malicious code
references:
    - https://twitter.com/JohnLaTwC/status/835149808817991680
    - https://blogs.technet.microsoft.com/pki/2006/11/30/basic-crl-checking-with-certutil/
    - https://www.trustedsec.com/2017/07/new-tool-release-nps_payload/
    - https://twitter.com/egre55/status/1087685529016193025
    - https://lolbas-project.github.io/lolbas/Binaries/Certutil/
author: Florian Roth (Nextron Systems), juju4, keepwatch
date: 2019-01-16
modified: 2023-02-15
tags:
    - attack.defense-evasion
    - attack.t1140
    - attack.command-and-control
    - attack.t1105
    - attack.s0160
    - attack.g0007
    - attack.g0010
    - attack.g0045
    - attack.g0049
    - attack.g0075
    - attack.g0096
logsource:
    category: process_creation
    product: windows
detection:
    process_creation:
        EventID: 4688
        Channel: Security
    selection_img:
        - NewProcessName|endswith: \certutil.exe
        - OriginalFileName: CertUtil.exe
    selection_cli:
        CommandLine|contains:
            - ' -decode '
            - ' -decodehex '
            - ' -urlcache '
            - ' -verifyctl '
            - ' -encode '
            - ' -exportPFX '
            - ' /decode '
            - ' /decodehex '
            - ' /urlcache '
            - ' /verifyctl '
            - ' /encode '
            - ' /exportPFX '
    condition: process_creation and (all of selection_*)
fields:
    - CommandLine
    - ParentCommandLine
falsepositives:
    - False positives depend on scripts and administrative tools used in the monitored environment
level: high
ruletype: Sigma

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

cb49524f-279e-4149-bc9f-d7386d335cd4

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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

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