Net WebClient Casing Anomalies

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

Detects PowerShell command line contents that include a suspicious abnormal casing in the Net.Webclient (e.g. nEt.WEbCliEnT) string as used in obfuscation techniques

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Net WebClient Casing Anomalies
id: c86133ad-4725-4bd0-8170-210788e0a7ba
status: test
description: Detects PowerShell command line contents that include a suspicious abnormal casing in the Net.Webclient (e.g. nEt.WEbCliEnT) string as used in obfuscation techniques
references:
    - https://app.any.run/tasks/b9040c63-c140-479b-ad59-f1bb56ce7a97/
author: Florian Roth (Nextron Systems)
date: 2022-05-24
modified: 2023-01-05
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_encoded:
        CommandLine|contains:
            - 'TgBlAFQALgB3AEUAQg'
            - '4AZQBUAC4AdwBFAEIA'
            - 'OAGUAVAAuAHcARQBCA'
            - 'bgBFAHQALgB3AGUAYg'
            - '4ARQB0AC4AdwBlAGIA'
            - 'uAEUAdAAuAHcAZQBiA'
            - 'TgBFAHQALgB3AGUAYg'
            - 'OAEUAdAAuAHcAZQBiA'
            - 'bgBlAFQALgB3AGUAYg'
            - '4AZQBUAC4AdwBlAGIA'
            - 'uAGUAVAAuAHcAZQBiA'
            - 'TgBlAFQALgB3AGUAYg'
            - 'OAGUAVAAuAHcAZQBiA'
            - 'bgBFAFQALgB3AGUAYg'
            - '4ARQBUAC4AdwBlAGIA'
            - 'uAEUAVAAuAHcAZQBiA'
            - 'bgBlAHQALgBXAGUAYg'
            - '4AZQB0AC4AVwBlAGIA'
            - 'uAGUAdAAuAFcAZQBiA'
            - 'bgBFAHQALgBXAGUAYg'
            - '4ARQB0AC4AVwBlAGIA'
            - 'uAEUAdAAuAFcAZQBiA'
            - 'TgBFAHQALgBXAGUAYg'
            - 'OAEUAdAAuAFcAZQBiA'
            - 'bgBlAFQALgBXAGUAYg'
            - '4AZQBUAC4AVwBlAGIA'
            - 'uAGUAVAAuAFcAZQBiA'
            - 'TgBlAFQALgBXAGUAYg'
            - 'OAGUAVAAuAFcAZQBiA'
            - 'bgBFAFQALgBXAGUAYg'
            - '4ARQBUAC4AVwBlAGIA'
            - 'uAEUAVAAuAFcAZQBiA'
            - 'bgBlAHQALgB3AEUAYg'
            - '4AZQB0AC4AdwBFAGIA'
            - 'uAGUAdAAuAHcARQBiA'
            - 'TgBlAHQALgB3AEUAYg'
            - 'OAGUAdAAuAHcARQBiA'
            - 'bgBFAHQALgB3AEUAYg'
            - '4ARQB0AC4AdwBFAGIA'
            - 'uAEUAdAAuAHcARQBiA'
            - 'TgBFAHQALgB3AEUAYg'
            - 'OAEUAdAAuAHcARQBiA'
            - 'bgBlAFQALgB3AEUAYg'
            - '4AZQBUAC4AdwBFAGIA'
            - 'uAGUAVAAuAHcARQBiA'
            - 'TgBlAFQALgB3AEUAYg'
            - 'OAGUAVAAuAHcARQBiA'
            - 'bgBFAFQALgB3AEUAYg'
            - '4ARQBUAC4AdwBFAGIA'
            - 'uAEUAVAAuAHcARQBiA'
            - 'TgBFAFQALgB3AEUAYg'
            - 'OAEUAVAAuAHcARQBiA'
            - 'bgBlAHQALgBXAEUAYg'
            - '4AZQB0AC4AVwBFAGIA'
            - 'uAGUAdAAuAFcARQBiA'
            - 'TgBlAHQALgBXAEUAYg'
            - 'OAGUAdAAuAFcARQBiA'
            - 'bgBFAHQALgBXAEUAYg'
            - '4ARQB0AC4AVwBFAGIA'
            - 'uAEUAdAAuAFcARQBiA'
            - 'TgBFAHQALgBXAEUAYg'
            - 'OAEUAdAAuAFcARQBiA'
            - 'bgBlAFQALgBXAEUAYg'
            - '4AZQBUAC4AVwBFAGIA'
            - 'uAGUAVAAuAFcARQBiA'
            - 'TgBlAFQALgBXAEUAYg'
            - 'OAGUAVAAuAFcARQBiA'
            - 'bgBFAFQALgBXAEUAYg'
            - '4ARQBUAC4AVwBFAGIA'
            - 'uAEUAVAAuAFcARQBiA'
            - 'TgBFAFQALgBXAEUAYg'
            - 'OAEUAVAAuAFcARQBiA'
            - 'bgBlAHQALgB3AGUAQg'
            - '4AZQB0AC4AdwBlAEIA'
            - 'uAGUAdAAuAHcAZQBCA'
            - 'TgBlAHQALgB3AGUAQg'
            - 'OAGUAdAAuAHcAZQBCA'
            - 'bgBFAHQALgB3AGUAQg'
            - '4ARQB0AC4AdwBlAEIA'
            - 'uAEUAdAAuAHcAZQBCA'
            - 'TgBFAHQALgB3AGUAQg'
            - 'OAEUAdAAuAHcAZQBCA'
            - 'bgBlAFQALgB3AGUAQg'
            - '4AZQBUAC4AdwBlAEIA'
            - 'uAGUAVAAuAHcAZQBCA'
            - 'TgBlAFQALgB3AGUAQg'
            - 'OAGUAVAAuAHcAZQBCA'
            - 'bgBFAFQALgB3AGUAQg'
            - '4ARQBUAC4AdwBlAEIA'
            - 'uAEUAVAAuAHcAZQBCA'
            - 'TgBFAFQALgB3AGUAQg'
            - 'OAEUAVAAuAHcAZQBCA'
            - 'bgBlAHQALgBXAGUAQg'
            - '4AZQB0AC4AVwBlAEIA'
            - 'uAGUAdAAuAFcAZQBCA'
            - 'TgBlAHQALgBXAGUAQg'
            - 'OAGUAdAAuAFcAZQBCA'
            - 'bgBFAHQALgBXAGUAQg'
            - '4ARQB0AC4AVwBlAEIA'
            - 'uAEUAdAAuAFcAZQBCA'
            - 'TgBFAHQALgBXAGUAQg'
            - 'OAEUAdAAuAFcAZQBCA'
            - 'bgBlAFQALgBXAGUAQg'
            - '4AZQBUAC4AVwBlAEIA'
            - 'uAGUAVAAuAFcAZQBCA'
            - 'TgBlAFQALgBXAGUAQg'
            - 'OAGUAVAAuAFcAZQBCA'
            - 'bgBFAFQALgBXAGUAQg'
            - '4ARQBUAC4AVwBlAEIA'
            - 'uAEUAVAAuAFcAZQBCA'
            - 'TgBFAFQALgBXAGUAQg'
            - 'OAEUAVAAuAFcAZQBCA'
            - 'bgBlAHQALgB3AEUAQg'
            - '4AZQB0AC4AdwBFAEIA'
            - 'uAGUAdAAuAHcARQBCA'
            - 'TgBlAHQALgB3AEUAQg'
            - 'OAGUAdAAuAHcARQBCA'
            - 'bgBFAHQALgB3AEUAQg'
            - '4ARQB0AC4AdwBFAEIA'
            - 'uAEUAdAAuAHcARQBCA'
            - 'TgBFAHQALgB3AEUAQg'
            - 'OAEUAdAAuAHcARQBCA'
            - 'bgBlAFQALgB3AEUAQg'
            - 'uAGUAVAAuAHcARQBCA'
            - 'bgBFAFQALgB3AEUAQg'
            - '4ARQBUAC4AdwBFAEIA'
            - 'uAEUAVAAuAHcARQBCA'
            - 'TgBFAFQALgB3AEUAQg'
            - 'OAEUAVAAuAHcARQBCA'
            - 'TgBlAHQALgBXAEUAQg'
            - '4AZQB0AC4AVwBFAEIA'
            - 'OAGUAdAAuAFcARQBCA'
            - 'bgBFAHQALgBXAEUAQg'
            - '4ARQB0AC4AVwBFAEIA'
            - 'uAEUAdAAuAFcARQBCA'
            - 'TgBFAHQALgBXAEUAQg'
            - 'OAEUAdAAuAFcARQBCA'
            - 'bgBlAFQALgBXAEUAQg'
            - '4AZQBUAC4AVwBFAEIA'
            - 'uAGUAVAAuAFcARQBCA'
            - 'TgBlAFQALgBXAEUAQg'
            - 'OAGUAVAAuAFcARQBCA'
            - 'bgBFAFQALgBXAEUAQg'
            - '4ARQBUAC4AVwBFAEIA'
            - 'uAEUAVAAuAFcARQBCA'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

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'

Stage 2: `selection_encoded`

selection_encoded:
    CommandLine|contains:
        - 'TgBlAFQALgB3AEUAQg'
        - '4AZQBUAC4AdwBFAEIA'
        - 'OAGUAVAAuAHcARQBCA'
        - 'bgBFAHQALgB3AGUAYg'
        - '4ARQB0AC4AdwBlAGIA'
        - 'uAEUAdAAuAHcAZQBiA'
        - 'TgBFAHQALgB3AGUAYg'
        - 'OAEUAdAAuAHcAZQBiA'
        - 'bgBlAFQALgB3AGUAYg'
        - '4AZQBUAC4AdwBlAGIA'
        - 'uAGUAVAAuAHcAZQBiA'
        - 'TgBlAFQALgB3AGUAYg'
        - 'OAGUAVAAuAHcAZQBiA'
        - 'bgBFAFQALgB3AGUAYg'
        - '4ARQBUAC4AdwBlAGIA'
        - 'uAEUAVAAuAHcAZQBiA'
        - 'bgBlAHQALgBXAGUAYg'
        - '4AZQB0AC4AVwBlAGIA'
        - 'uAGUAdAAuAFcAZQBiA'
        - 'bgBFAHQALgBXAGUAYg'
        - '4ARQB0AC4AVwBlAGIA'
        - 'uAEUAdAAuAFcAZQBiA'
        - 'TgBFAHQALgBXAGUAYg'
        - 'OAEUAdAAuAFcAZQBiA'
        - 'bgBlAFQALgBXAGUAYg'
        - '4AZQBUAC4AVwBlAGIA'
        - 'uAGUAVAAuAFcAZQBiA'
        - 'TgBlAFQALgBXAGUAYg'
        - 'OAGUAVAAuAFcAZQBiA'
        - 'bgBFAFQALgBXAGUAYg'
        - '4ARQBUAC4AVwBlAGIA'
        - 'uAEUAVAAuAFcAZQBiA'
        - 'bgBlAHQALgB3AEUAYg'
        - '4AZQB0AC4AdwBFAGIA'
        - 'uAGUAdAAuAHcARQBiA'
        - 'TgBlAHQALgB3AEUAYg'
        - 'OAGUAdAAuAHcARQBiA'
        - 'bgBFAHQALgB3AEUAYg'
        - '4ARQB0AC4AdwBFAGIA'
        - 'uAEUAdAAuAHcARQBiA'
        - 'TgBFAHQALgB3AEUAYg'
        - 'OAEUAdAAuAHcARQBiA'
        - 'bgBlAFQALgB3AEUAYg'
        - '4AZQBUAC4AdwBFAGIA'
        - 'uAGUAVAAuAHcARQBiA'
        - 'TgBlAFQALgB3AEUAYg'
        - 'OAGUAVAAuAHcARQBiA'
        - 'bgBFAFQALgB3AEUAYg'
        - '4ARQBUAC4AdwBFAGIA'
        - 'uAEUAVAAuAHcARQBiA'
        - 'TgBFAFQALgB3AEUAYg'
        - 'OAEUAVAAuAHcARQBiA'
        - 'bgBlAHQALgBXAEUAYg'
        - '4AZQB0AC4AVwBFAGIA'
        - 'uAGUAdAAuAFcARQBiA'
        - 'TgBlAHQALgBXAEUAYg'
        - 'OAGUAdAAuAFcARQBiA'
        - 'bgBFAHQALgBXAEUAYg'
        - '4ARQB0AC4AVwBFAGIA'
        - 'uAEUAdAAuAFcARQBiA'
        - 'TgBFAHQALgBXAEUAYg'
        - 'OAEUAdAAuAFcARQBiA'
        - 'bgBlAFQALgBXAEUAYg'
        - '4AZQBUAC4AVwBFAGIA'
        - 'uAGUAVAAuAFcARQBiA'
        - 'TgBlAFQALgBXAEUAYg'
        - 'OAGUAVAAuAFcARQBiA'
        - 'bgBFAFQALgBXAEUAYg'
        - '4ARQBUAC4AVwBFAGIA'
        - 'uAEUAVAAuAFcARQBiA'
        - 'TgBFAFQALgBXAEUAYg'
        - 'OAEUAVAAuAFcARQBiA'
        - 'bgBlAHQALgB3AGUAQg'
        - '4AZQB0AC4AdwBlAEIA'
        - 'uAGUAdAAuAHcAZQBCA'
        - 'TgBlAHQALgB3AGUAQg'
        - 'OAGUAdAAuAHcAZQBCA'
        - 'bgBFAHQALgB3AGUAQg'
        - '4ARQB0AC4AdwBlAEIA'
        - 'uAEUAdAAuAHcAZQBCA'
        - 'TgBFAHQALgB3AGUAQg'
        - 'OAEUAdAAuAHcAZQBCA'
        - 'bgBlAFQALgB3AGUAQg'
        - '4AZQBUAC4AdwBlAEIA'
        - 'uAGUAVAAuAHcAZQBCA'
        - 'TgBlAFQALgB3AGUAQg'
        - 'OAGUAVAAuAHcAZQBCA'
        - 'bgBFAFQALgB3AGUAQg'
        - '4ARQBUAC4AdwBlAEIA'
        - 'uAEUAVAAuAHcAZQBCA'
        - 'TgBFAFQALgB3AGUAQg'
        - 'OAEUAVAAuAHcAZQBCA'
        - 'bgBlAHQALgBXAGUAQg'
        - '4AZQB0AC4AVwBlAEIA'
        - 'uAGUAdAAuAFcAZQBCA'
        - 'TgBlAHQALgBXAGUAQg'
        - 'OAGUAdAAuAFcAZQBCA'
        - 'bgBFAHQALgBXAGUAQg'
        - '4ARQB0AC4AVwBlAEIA'
        - 'uAEUAdAAuAFcAZQBCA'
        - 'TgBFAHQALgBXAGUAQg'
        - 'OAEUAdAAuAFcAZQBCA'
        - 'bgBlAFQALgBXAGUAQg'
        - '4AZQBUAC4AVwBlAEIA'
        - 'uAGUAVAAuAFcAZQBCA'
        - 'TgBlAFQALgBXAGUAQg'
        - 'OAGUAVAAuAFcAZQBCA'
        - 'bgBFAFQALgBXAGUAQg'
        - '4ARQBUAC4AVwBlAEIA'
        - 'uAEUAVAAuAFcAZQBCA'
        - 'TgBFAFQALgBXAGUAQg'
        - 'OAEUAVAAuAFcAZQBCA'
        - 'bgBlAHQALgB3AEUAQg'
        - '4AZQB0AC4AdwBFAEIA'
        - 'uAGUAdAAuAHcARQBCA'
        - 'TgBlAHQALgB3AEUAQg'
        - 'OAGUAdAAuAHcARQBCA'
        - 'bgBFAHQALgB3AEUAQg'
        - '4ARQB0AC4AdwBFAEIA'
        - 'uAEUAdAAuAHcARQBCA'
        - 'TgBFAHQALgB3AEUAQg'
        - 'OAEUAdAAuAHcARQBCA'
        - 'bgBlAFQALgB3AEUAQg'
        - 'uAGUAVAAuAHcARQBCA'
        - 'bgBFAFQALgB3AEUAQg'
        - '4ARQBUAC4AdwBFAEIA'
        - 'uAEUAVAAuAHcARQBCA'
        - 'TgBFAFQALgB3AEUAQg'
        - 'OAEUAVAAuAHcARQBCA'
        - 'TgBlAHQALgBXAEUAQg'
        - '4AZQB0AC4AVwBFAEIA'
        - 'OAGUAdAAuAFcARQBCA'
        - 'bgBFAHQALgBXAEUAQg'
        - '4ARQB0AC4AVwBFAEIA'
        - 'uAEUAdAAuAFcARQBCA'
        - 'TgBFAHQALgBXAEUAQg'
        - 'OAEUAdAAuAFcARQBCA'
        - 'bgBlAFQALgBXAEUAQg'
        - '4AZQBUAC4AVwBFAEIA'
        - 'uAGUAVAAuAFcARQBCA'
        - 'TgBlAFQALgBXAEUAQg'
        - 'OAGUAVAAuAFcARQBCA'
        - 'bgBFAFQALgBXAEUAQg'
        - '4ARQBUAC4AVwBFAEIA'
        - 'uAEUAVAAuAFcARQBCA'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`4ARQB0AC4AVwBFAEIA` `4ARQB0AC4AVwBFAGIA` `4ARQB0AC4AVwBlAEIA` `4ARQB0AC4AVwBlAGIA` `4ARQB0AC4AdwBFAEIA` `4ARQB0AC4AdwBFAGIA` `4ARQB0AC4AdwBlAEIA` `4ARQB0AC4AdwBlAGIA` `4ARQBUAC4AVwBFAEIA` `4ARQBUAC4AVwBFAGIA` `4ARQBUAC4AVwBlAEIA` `4ARQBUAC4AVwBlAGIA` `4ARQBUAC4AdwBFAEIA` `4ARQBUAC4AdwBFAGIA` `4ARQBUAC4AdwBlAEIA` `4ARQBUAC4AdwBlAGIA` `4AZQB0AC4AVwBFAEIA` `4AZQB0AC4AVwBFAGIA` `4AZQB0AC4AVwBlAEIA` `4AZQB0AC4AVwBlAGIA` `4AZQB0AC4AdwBFAEIA` `4AZQB0AC4AdwBFAGIA` `4AZQB0AC4AdwBlAEIA` `4AZQBUAC4AVwBFAEIA` `4AZQBUAC4AVwBFAGIA` `4AZQBUAC4AVwBlAEIA` `4AZQBUAC4AVwBlAGIA` `4AZQBUAC4AdwBFAEIA` `4AZQBUAC4AdwBFAGIA` `4AZQBUAC4AdwBlAEIA` `4AZQBUAC4AdwBlAGIA` `OAEUAVAAuAFcARQBiA` `OAEUAVAAuAFcAZQBCA` `OAEUAVAAuAHcARQBCA` `OAEUAVAAuAHcARQBiA` `OAEUAVAAuAHcAZQBCA` `OAEUAdAAuAFcARQBCA` `OAEUAdAAuAFcARQBiA` `OAEUAdAAuAFcAZQBCA` `OAEUAdAAuAFcAZQBiA` +105 more values (see full rule source)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\powershell.exe` corpus 179 (sigma 178, kusto 1) `\pwsh.exe` corpus 165 (sigma 164, kusto 1)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`PowerShell.EXE` corpus 138 (sigma 84, splunk 30, elastic 24) `pwsh.dll` corpus 112 (sigma 79, splunk 30, elastic 3)	`field:"OriginalFileName" kind:eq`