Suspicious Windows regsvr32 Command-Line Uses FTP/HTTP to Register Remote Components

Alerts on regsvr32 command lines using /i flags with ftp/http content, consistent with remote DLL registration.

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title: Suspicious Windows regsvr32 Command-Line Uses FTP/HTTP to Register Remote Components
id: b7ed83c8-33ce-4c8f-b5fb-e5ac766800f3
related:
  - id: 8e2b24c9-4add-46a0-b4bb-0057b4e6187d
    type: obsolete
  - id: 867356ee-9352-41c9-a8f2-1be690d78216
    type: derived
status: test
description: This rule flags regsvr32.exe executions where the command line includes image registration flags ('/i' or ' -i') and references remote content over FTP or HTTP. Attackers may use regsvr32 to stealthily fetch and register attacker-controlled DLLs from network locations. It relies on Windows process creation telemetry, matching the process image and specific substrings within the command line.
references:
  - https://twitter.com/mrd0x/status/1461041276514623491
  - https://twitter.com/tccontre18/status/1480950986650832903
  - https://lolbas-project.github.io/lolbas/Binaries/Regsvr32/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_regsvr32_network_pattern.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2023-05-24
modified: 2023-05-26
tags:
  - attack.stealth
  - attack.t1218.010
logsource:
  category: process_creation
  product: windows
detection:
  selection_img:
    - Image|endswith: \regsvr32.exe
    - OriginalFileName: REGSVR32.EXE
  selection_flag:
    CommandLine|contains:
      - " /i"
      - " -i"
  selection_protocol:
    CommandLine|contains:
      - ftp
      - http
  condition: all of selection_*
falsepositives:
  - Unknown
level: medium
license: DRL-1.1

What it detects

This rule flags regsvr32.exe executions where the command line includes image registration flags ('/i' or ' -i') and references remote content over FTP or HTTP. Attackers may use regsvr32 to stealthily fetch and register attacker-controlled DLLs from network locations. It relies on Windows process creation telemetry, matching the process image and specific substrings within the command line.

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.