Windows regsvr32 Launches AppData Local DLLs Referencing DllEntry

title: Windows regsvr32 Launches AppData Local DLLs Referencing DllEntry
id: 6048aaf1-982b-49b0-b42a-9d5e39db5e5d
status: test
description: This rule flags process creation events where regsvr32 is invoked with command-line arguments pointing to a DLL located under AppData\Local and referencing DllEntry. Attackers may use regsvr32 to load a malicious DLL while blending into legitimate signed Windows utility execution. The detection relies on Windows process creation telemetry, specifically the full command line contents.
references:
  - https://pbs.twimg.com/media/EF3yLGoWkAEGeLa?format=jpg
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2019/TA/APC-C-12/proc_creation_win_apt_aptc12_bluemushroom.yml
author: Florian Roth (Nextron Systems), Tim Shelton, Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2019-10-02
modified: 2023-03-29
tags:
  - attack.stealth
  - attack.t1218.010
  - detection.emerging-threats
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains|all:
      - regsvr32
      - \AppData\Local\
      - .dll
      - ",DllEntry"
  condition: selection
falsepositives:
  - Unknown
level: medium
license: DRL-1.1
related:
  - id: bd70d3f8-e60e-4d25-89f0-0b5a9cff20e0
    type: derived