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Detection rules › Sigma

Suspicious Child Process Of BgInfo.EXE

Status
test
Severity
high
Log source
product windows, category process_creation
Author
Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects suspicious child processes of "BgInfo.exe" which could be a sign of potential abuse of the binary to proxy execution via external VBScript

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.005 Command and Scripting Interpreter: Visual Basic
StealthT1202 Indirect Command Execution, T1218 System Binary Proxy Execution

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

title: Suspicious Child Process Of BgInfo.EXE
id: 811f459f-9231-45d4-959a-0266c6311987
related:
    - id: aaf46cdc-934e-4284-b329-34aa701e3771
      type: similar
status: test
description: Detects suspicious child processes of "BgInfo.exe" which could be a sign of potential abuse of the binary to proxy execution via external VBScript
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Bginfo/
    - https://oddvar.moe/2017/05/18/bypassing-application-whitelisting-with-bginfo/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-08-16
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.005
    - attack.t1218
    - attack.t1202
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent:
        ParentImage|endswith:
            - '\bginfo.exe'
            - '\bginfo64.exe'
    selection_child:
        - Image|endswith:
              - '\calc.exe'
              - '\cmd.exe'
              - '\cscript.exe'
              - '\mshta.exe'
              - '\notepad.exe'
              - '\powershell.exe'
              - '\pwsh.exe'
              - '\wscript.exe'
        - Image|contains:
              - '\AppData\Local\'
              - '\AppData\Roaming\'
              - ':\Users\Public\'
              - ':\Temp\'
              - ':\Windows\Temp\'
              - ':\PerfLogs\'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_parent

selection_parent:
    ParentImage|endswith:
        - '\bginfo.exe'
        - '\bginfo64.exe'

Stage 2: selection_child

selection_child:
    - Image|endswith:
          - '\calc.exe'
          - '\cmd.exe'
          - '\cscript.exe'
          - '\mshta.exe'
          - '\notepad.exe'
          - '\powershell.exe'
          - '\pwsh.exe'
          - '\wscript.exe'
    - Image|contains:
          - '\AppData\Local\'
          - '\AppData\Roaming\'
          - ':\Users\Public\'
          - ':\Temp\'
          - ':\Windows\Temp\'
          - ':\PerfLogs\'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
Imageends_with
  • \calc.exe corpus 13 (sigma 13)
  • \cmd.exe corpus 130 (sigma 130)
  • \cscript.exe corpus 73 (sigma 73)
  • \mshta.exe corpus 67 (sigma 67)
  • \notepad.exe corpus 9 (sigma 9)
  • \powershell.exe corpus 182 (sigma 182)
  • \pwsh.exe corpus 168 (sigma 168)
  • \wscript.exe corpus 75 (sigma 75)
Imagematch
  • :\PerfLogs\ corpus 10 (sigma 10)
  • :\Temp\ corpus 13 (sigma 13)
  • :\Users\Public\ corpus 15 (sigma 15)
  • :\Windows\Temp\ corpus 9 (sigma 9)
  • \AppData\Local\
  • \AppData\Roaming\ corpus 2 (sigma 2)
ParentImageends_with
  • \bginfo.exe corpus 2 (sigma 2)
  • \bginfo64.exe corpus 2 (sigma 2)