Suspicious Cross-User Process Spawn

Title: Suspicious Cross-User Process Spawn
Status: experimental
Description:Detects suspicious spawning of a process under a different user context than the parent process. Processes such as notepad.exe, calculator etc. are generally spawned under the same user context and also they are often targeted as sacrificial process or decoy process to check successful privilege escalation.
References:
  -https://github.com/MSNightmare/LegacyHive
  -https://git.projectnightcrawler.dev/NightmareEclipse/LegacyHive
Author: Swachchhanda Shrawan Poudel (Nextron Systems)
Date: 2026-07-23
modified:None
Tags:

• -'attack.privilege-escalation'
• -'attack.stealth'
• -'attack.t1055'
• -'attack.t1134'

Logsource:

• category: process_creation
• product: windows

Detection:
  selection:
    Image|endswith:
      -'\notepad.exe'
      -'\calc.exe'
      -'\mspaint.exe'
      -'\wordpad.exe'
      -'\write.exe'

  filter_main_same_user:
    User|fieldref: 'ParentUser'
  filter_optional_user_null:
    User: 'None'
  filter_optional_parent_null:
    ParentUser: 'None'
  filter_optional_empty_user:
    - ParentUser:
      - ''
      - '-'
    - User:
      - ''
      - '-'
  condition:selection and not 1 of filter_main_* and not 1 of filter_optional_*
Falsepositives:
  -RunAs usage spawning one of the listed binaries under a different account
Level: medium