Windows Process Execution of Regasm/Regsvcs from Uncommon Directories

Alerts on Regasm/Regsvcs executions from commonly abused non-standard directories using process creation image and command line fields.

FreeUnreviewedSigmamediumv1

windows-process-execution-of-regasm-regsvcs-from-uncommon-directories-cc368ed0

title: Windows Process Execution of Regasm/Regsvcs from Uncommon Directories
id: 2ca73eca-854d-4869-930f-7ff5e098e545
related:
  - id: e9f8f8cc-07cc-4e81-b724-f387db9175e4
    type: derived
  - id: cc368ed0-2411-45dc-a222-510ace303cb2
    type: derived
status: test
description: This rule flags process creations where Regasm.exe or Regsvcs.exe is executed from specific, potentially suspicious directory paths (e.g., Temp, Startup, PerfLogs, Users\Public, and Windows Temp). Attackers may use these Windows registration utilities to execute or stage components in a way that blends into normal system behavior. It relies on Windows process creation telemetry containing the image name and the full command line for directory/path context.
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/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_regasm_regsvcs_uncommon_location_execution.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
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:
      - \AppData\Local\Temp\
      - \Microsoft\Windows\Start Menu\Programs\Startup\
      - \PerfLogs\
      - \Users\Public\
      - \Windows\Temp\
  condition: all of selection_*
falsepositives:
  - Unknown
level: medium
license: DRL-1.1

What it detects

This rule flags process creations where Regasm.exe or Regsvcs.exe is executed from specific, potentially suspicious directory paths (e.g., Temp, Startup, PerfLogs, Users\Public, and Windows Temp). Attackers may use these Windows registration utilities to execute or stage components in a way that blends into normal system behavior. It relies on Windows process creation telemetry containing the image name and the full command line for directory/path context.

Known false positives

Unknown

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.