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Detection rules › Sigma

Suspicious XOR Encoded PowerShell Command

Status
test
Severity
medium
Log source
product windows, category process_creation
Author
Sami Ruohonen, Harish Segar, Tim Shelton, Teymur Kheirkhabarov, Vasiliy Burov, oscd.community, Nasreddine Bencherchali
Source
github.com/SigmaHQ/sigma

Detects presence of a potentially xor encoded powershell command

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.001 Command and Scripting Interpreter: PowerShell
StealthT1027 Obfuscated Files or Information, T1140 Deobfuscate/Decode Files or Information

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

title: Suspicious XOR Encoded PowerShell Command
id: bb780e0c-16cf-4383-8383-1e5471db6cf9
related:
    - id: 5b572dcf-254b-425c-a8c5-d9af6bea35a6
      type: obsolete
status: test
description: Detects presence of a potentially xor encoded powershell command
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=65
    - https://redcanary.com/blog/yellow-cockatoo/
    - https://zero2auto.com/2020/05/19/netwalker-re/
    - https://mez0.cc/posts/cobaltstrike-powershell-exec/
author: Sami Ruohonen, Harish Segar, Tim Shelton, Teymur Kheirkhabarov, Vasiliy Burov, oscd.community, Nasreddine Bencherchali
date: 2018-09-05
modified: 2023-01-30
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.001
    - attack.t1140
    - attack.t1027
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
        - Description: 'Windows PowerShell'
        - Product: 'PowerShell Core 6'
    selection_cli_xor:
        CommandLine|contains: 'bxor'
    selection_cli_other:
        CommandLine|contains:
            - 'ForEach'
            - 'for('
            - 'for '
            - '-join '
            - "-join'"
            - '-join"'
            - '-join`'
            - '::Join'
            - '[char]'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: condition

all of selection_*

Stage 1: selection_img

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'
    - Description: 'Windows PowerShell'
    - Product: 'PowerShell Core 6'

Stage 2: selection_cli_xor

selection_cli_xor:
    CommandLine|contains: 'bxor'

Stage 3: selection_cli_other

selection_cli_other:
    CommandLine|contains:
        - 'ForEach'
        - 'for('
        - 'for '
        - '-join '
        - "-join'"
        - '-join"'
        - '-join`'
        - '::Join'
        - '[char]'

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
CommandLinematch
  • -join
  • -join"
  • -join'
  • -join`
  • ::Join
  • ForEach
  • [char]
  • bxor
  • for corpus 2 (sigma 2)
  • for(
Descriptioneq
  • Windows PowerShell corpus 2 (sigma 2)
Imageends_with
  • \powershell.exe corpus 182 (sigma 182)
  • \pwsh.exe corpus 168 (sigma 168)
OriginalFileNameeq
  • PowerShell.EXE corpus 120 (sigma 84, splunk 30, elastic 6)
  • pwsh.dll corpus 112 (sigma 79, splunk 30, elastic 3)
Producteq
  • PowerShell Core 6 corpus 3 (sigma 3)