Suspicious New Instance Of An Office COM Object

SIGMA detection rule by Nasreddine Bencherchali (Nextron Systems) · NOASSERTION

Detects an svchost process spawning an instance of an office application. This happens when the initial word application creates an instance of one of the Office COM objects such as 'Word.Application', 'Excel.Application', etc. This can be used by malicious actors to create malicious Office documents with macros on the fly. (See vba2clr project in the references)

title: Suspicious New Instance Of An Office COM Object
id: 9bdaf1e9-fdef-443b-8081-4341b74a7e28
status: test
description: |
    Detects an svchost process spawning an instance of an office application. This happens when the initial word application creates an instance of one of the Office COM objects such as 'Word.Application', 'Excel.Application', etc.
    This can be used by malicious actors to create malicious Office documents with macros on the fly. (See vba2clr project in the references)
references:
    - https://learn.microsoft.com/en-us/previous-versions/office/troubleshoot/office-developer/automate-word-create-file-using-visual-basic
    - https://github.com/med0x2e/vba2clr
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-10-13
modified: 2023-12-19
tags:
    - attack.execution
    - detection.threat-hunting
    - attack.stealth
logsource:
    product: windows
    category: process_creation
detection:
    selection:
        ParentImage|endswith: '\svchost.exe'
        Image|endswith:
            - '\eqnedt32.exe'
            - '\excel.exe'
            - '\msaccess.exe'
            - '\mspub.exe'
            - '\powerpnt.exe'
            - '\visio.exe'
            - '\winword.exe'
    condition: selection
falsepositives:
    - Legitimate usage of office automation via scripting
level: medium

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

e842849b-4aa6-4ffb-8ce1-84234e2d06d9

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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 ]]

[[ currentRule.title ]]

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