Excel Proxy Executing Regsvr32 With Payload

SIGMA detection rule by Vadim Khrykov (ThreatIntel), Cyb3rEng (Rule) · NOASSERTION

Excel called wmic to finally proxy execute regsvr32 with the payload. An attacker wanted to break suspicious parent-child chain (Office app spawns LOLBin). But we have command-line in the event which allow us to "restore" this suspicious parent-child chain and detect it. Monitor process creation with "wmic process call create" and LOLBins in command-line with parent Office application processes.

title: Excel Proxy Executing Regsvr32 With Payload
id: 9d1c72f5-43f0-4da5-9320-648cf2099dd0
status: deprecated
description: |
  Excel called wmic to finally proxy execute regsvr32 with the payload.
  An attacker wanted to break suspicious parent-child chain (Office app spawns LOLBin).
  But we have command-line in the event which allow us to "restore" this suspicious parent-child chain and detect it.
  Monitor process creation with "wmic process call create" and LOLBins in command-line with parent Office application processes.
references:
    - https://thedfirreport.com/2021/03/29/sodinokibi-aka-revil-ransomware/
    - https://github.com/vadim-hunter/Detection-Ideas-Rules/blob/02bcbfc2bfb8b4da601bb30de0344ae453aa1afe/Threat%20Intelligence/The%20DFIR%20Report/20210329_Sodinokibi_(aka_REvil)_Ransomware.yaml
author: 'Vadim Khrykov (ThreatIntel), Cyb3rEng (Rule)'
date: 2021/08/23
modified: 2022/12/02
tags:
    - attack.t1204.002
    - attack.t1047
    - attack.t1218.010
    - attack.execution
    - attack.defense_evasion
logsource:
    product: windows
    category: process_creation
detection:
    #useful_information: add more LOLBins to the rules logic of your choice.
    selection_img:
        - Image|endswith: '\wbem\WMIC.exe'
        - OriginalFileName: 'wmic.exe'
    selection_other:
        CommandLine|contains:
            - 'regsvr32'
            - 'rundll32'
            - 'msiexec'
            - 'mshta'
            - 'verclsid'
        ParentImage|endswith:
            - '\winword.exe'
            - '\excel.exe'
            - '\powerpnt.exe'
        CommandLine|contains|all:
            - 'process'
            - 'create'
            - 'call'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

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

5f9c404f-3723-458b-90db-c10457d8264f

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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.

Rejected pattern present

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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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