Potentially Suspicious Desktop Background Change Using Reg.EXE

Title: Potentially Suspicious Desktop Background Change Using Reg.EXE
Status: test
Description:Detects the execution of "reg.exe" to alter registry keys that would replace the user's desktop background. This is a common technique used by malware to change the desktop background to a ransom note or other image.
References:
  -https://www.attackiq.com/2023/09/20/emulating-rhysida/
  -https://research.checkpoint.com/2023/the-rhysida-ransomware-activity-analysis-and-ties-to-vice-society/
  -https://www.trendmicro.com/en_us/research/23/h/an-overview-of-the-new-rhysida-ransomware.html
  -https://www.virustotal.com/gui/file/a864282fea5a536510ae86c77ce46f7827687783628e4f2ceb5bf2c41b8cd3c6/behavior
  -https://admx.help/?Category=Windows_10_2016&Policy=Microsoft.Policies.WindowsDesktop::Wallpaper
  -https://admx.help/?Category=Windows_10_2016&Policy=Microsoft.Policies.ControlPanelDisplay::CPL_Personalization_NoDesktopBackgroundUI
Author: Stephen Lincoln @slincoln-aiq (AttackIQ)
Date: 2023-12-21
modified:None
Tags:

• -'attack.persistence'
• -'attack.impact'
• -'attack.defense-impairment'
• -'attack.t1112'
• -'attack.t1491.001'

Logsource:

• product: windows
• category: process_creation

Detection:
  selection_reg_img:
Image|endswith:'\reg.exe' OriginalFileName:'reg.exe'   selection_reg_flag:
    CommandLine|contains: 'add'
  selection_keys:
    CommandLine|contains:
      -'Control Panel\Desktop'
      -'CurrentVersion\Policies\ActiveDesktop'
      -'CurrentVersion\Policies\System'

  selection_cli_reg_1:
    CommandLine|contains|all:
      -'/v NoChangingWallpaper'
      -'/d 1'

  selection_cli_reg_2:
    CommandLine|contains|all:
      -'/v Wallpaper'
      -'/t REG_SZ'

  selection_cli_reg_3:
    CommandLine|contains|all:
      -'/v WallpaperStyle'
      -'/d 2'

  condition:all of selection_reg_* and selection_keys and 1 of selection_cli_reg_*
Falsepositives:
  -Administrative scripts that change the desktop background to a company logo or other image.
Level: medium