Bad Opsec Defaults Sacrificial Processes With Improper Arguments — Sigma Rule

Rule metadata and linked tags

Author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems). Source status: test; severity: high. Source dates: 2020-10-23 / 2024-08-15.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 1d4559cda59ded2d2895b084b2f9e26fc04e5f7dc6f45c0dcd1ba5f54fbbac52

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Bad Opsec Defaults Sacrificial Processes With Improper Arguments
id: a7c3d773-caef-227e-a7e7-c2f13c622329
related:
    - id: f5647edc-a7bf-4737-ab50-ef8c60dc3add
      type: obsolete
status: test
description: |
    Detects attackers using tooling with bad opsec defaults.
    E.g. spawning a sacrificial process to inject a capability into the process without taking into account how the process is normally run.
    One trivial example of this is using rundll32.exe without arguments as a sacrificial process (default in CS, now highlighted by c2lint), running WerFault without arguments (Kraken - credit am0nsec), and other examples.
references:
    - https://blog.malwarebytes.com/malwarebytes-news/2020/10/kraken-attack-abuses-wer-service/
    - https://www.cobaltstrike.com/help-opsec
    - https://twitter.com/CyberRaiju/status/1251492025678983169
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/regsvr32
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/rundll32
    - https://learn.microsoft.com/en-us/dotnet/framework/tools/regasm-exe-assembly-registration-tool
    - https://learn.microsoft.com/en-us/dotnet/framework/tools/regsvcs-exe-net-services-installation-tool
author: Oleg Kolesnikov @securonix invrep_de, oscd.community, Florian Roth (Nextron Systems), Christian Burkard (Nextron Systems)
date: 2020-10-23
modified: 2024-08-15
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection_werfault:
        Image|endswith: '\WerFault.exe'
        CommandLine|endswith: 'WerFault.exe'
    selection_rundll32:
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    selection_regsvcs:
        Image|endswith: '\regsvcs.exe'
        CommandLine|endswith: 'regsvcs.exe'
    selection_regasm:
        Image|endswith: '\regasm.exe'
        CommandLine|endswith: 'regasm.exe'
    selection_regsvr32:
        Image|endswith: '\regsvr32.exe'
        CommandLine|endswith: 'regsvr32.exe'
    filter_optional_edge_update:
        ParentImage|contains: '\AppData\Local\Microsoft\EdgeUpdate\Install\{'
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    filter_optional_chromium_installer:
        # As reported in https://github.com/SigmaHQ/sigma/issues/4570 and others
        ParentImage|contains:
            - '\AppData\Local\BraveSoftware\Brave-Browser\Application\'
            - '\AppData\Local\Google\Chrome\Application\'
        ParentImage|endswith: '\Installer\setup.exe'
        ParentCommandLine|contains: '--uninstall '
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith: 'rundll32.exe'
    condition: 1 of selection_* and not 1 of filter_optional_*
falsepositives:
    - Unlikely
level: high

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://blog.malwarebytes.com/malwarebytes-news/2020/10/kraken-attack-abuses-wer-service/
• https://www.cobaltstrike.com/help-opsec
• https://twitter.com/CyberRaiju/status/1251492025678983169
• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/regsvr32
• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/rundll32
• https://learn.microsoft.com/en-us/dotnet/framework/tools/regasm-exe-assembly-registration-tool
• https://learn.microsoft.com/en-us/dotnet/framework/tools/regsvcs-exe-net-services-installation-tool