Potentially Suspicious Execution Of Regasm/Regsvcs From Uncommon Location

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

Detects potentially suspicious execution of the Regasm/Regsvcs utilities from a potentially suspicious location

title: Potentially Suspicious Execution Of Regasm/Regsvcs From Uncommon Location
id: cc368ed0-2411-45dc-a222-510ace303cb2
related:
    - id: e9f8f8cc-07cc-4e81-b724-f387db9175e4
      type: derived
status: test
description: Detects potentially suspicious execution of the Regasm/Regsvcs utilities from a potentially suspicious location
references:
    - https://www.fortiguard.com/threat-signal-report/4718?s=09
    - https://lolbas-project.github.io/lolbas/Binaries/Regasm/
    - https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-25
modified: 2023-02-13
tags:
    - attack.stealth
    - attack.t1218.009
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\Regsvcs.exe'
              - '\Regasm.exe'
        - OriginalFileName:
              - 'RegSvcs.exe'
              - 'RegAsm.exe'
    selection_dir:
        CommandLine|contains:
            # Note: Add more potentially suspicious directories
            - '\AppData\Local\Temp\'
            - '\Microsoft\Windows\Start Menu\Programs\Startup\'
            - '\PerfLogs\'
            - '\Users\Public\'
            - '\Windows\Temp\'
            # - '\Desktop\'
            # - '\Downloads\'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

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

758a2b43-1ba3-410d-884d-e74e1548d74b

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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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