Base64 encoded Windows process command-lines

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Id	ca67c83e-7fff-4127-a3e3-1af66d6d4cad
Rulename	Base64 encoded Windows process command-lines
Description	Identifies instances of a base64-encoded PE file header seen in the process command line parameter.
Severity	Medium
Tactics	Execution DefenseEvasion
Techniques	T1059 T1027 T1140
Required data connectors	SecurityEvents WindowsForwardedEvents WindowsSecurityEvents
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Endpoint Threat Protection Essentials/Analytic Rules/base64_encoded_pefile.yaml
Version	1.1.4
Arm template	ca67c83e-7fff-4127-a3e3-1af66d6d4cad.json

KQL

let ProcessCreationEvents=(union isfuzzy=true
(SecurityEvent
| where EventID==4688
| where isnotempty(CommandLine)
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,
FileName = Process, CommandLine, ParentProcessName
),
(WindowsEvent
| where EventID==4688
| where EventData has "TVqQAAMAAAAEAAA"
| extend CommandLine = tostring(EventData.CommandLine)
| where isnotempty(CommandLine)
| extend ParentProcessName = tostring(EventData.ParentProcessName)
| extend NewProcessName = tostring(EventData.NewProcessName)
| extend Process=tostring(split(NewProcessName, '\\')[-1])
| extend SubjectUserName = tostring(EventData.SubjectUserName)
| extend SubjectDomainName = tostring(EventData.SubjectDomainName)
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,
FileName = Process, CommandLine, ParentProcessName));
ProcessCreationEvents
| where CommandLine contains "TVqQAAMAAAAEAAA"
| extend HostName = iif(Computer has '.',substring(Computer,0,indexof(Computer,'.')),Computer) , DnsDomain = iif(Computer has '.',substring(Computer,indexof(Computer,'.')+1),'')

YAML

severity: Medium
relevantTechniques:
- T1059
- T1027
- T1140
queryFrequency: 1d
kind: Scheduled
version: 1.1.4
name: Base64 encoded Windows process command-lines
triggerOperator: gt
description: |
    'Identifies instances of a base64-encoded PE file header seen in the process command line parameter.'
queryPeriod: 1d
query: |
  let ProcessCreationEvents=(union isfuzzy=true
  (SecurityEvent
  | where EventID==4688
  | where isnotempty(CommandLine)
  | summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,
  FileName = Process, CommandLine, ParentProcessName
  ),
  (WindowsEvent
  | where EventID==4688
  | where EventData has "TVqQAAMAAAAEAAA"
  | extend CommandLine = tostring(EventData.CommandLine)
  | where isnotempty(CommandLine)
  | extend ParentProcessName = tostring(EventData.ParentProcessName)
  | extend NewProcessName = tostring(EventData.NewProcessName)
  | extend Process=tostring(split(NewProcessName, '\\')[-1])
  | extend SubjectUserName = tostring(EventData.SubjectUserName)
  | extend SubjectDomainName = tostring(EventData.SubjectDomainName)
  | summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,
  FileName = Process, CommandLine, ParentProcessName));
  ProcessCreationEvents
  | where CommandLine contains "TVqQAAMAAAAEAAA"
  | extend HostName = iif(Computer has '.',substring(Computer,0,indexof(Computer,'.')),Computer) , DnsDomain = iif(Computer has '.',substring(Computer,indexof(Computer,'.')+1),'')  
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: Account
    identifier: Name
- entityType: Host
  fieldMappings:
  - columnName: Computer
    identifier: FullName
  - columnName: HostName
    identifier: HostName
  - columnName: DnsDomain
    identifier: DnsDomain
tactics:
- Execution
- DefenseEvasion
status: Available
triggerThreshold: 0
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Endpoint Threat Protection Essentials/Analytic Rules/base64_encoded_pefile.yaml
id: ca67c83e-7fff-4127-a3e3-1af66d6d4cad
requiredDataConnectors:
- dataTypes:
  - SecurityEvent
  connectorId: SecurityEvents
- dataTypes:
  - SecurityEvent
  connectorId: WindowsSecurityEvents
- dataTypes:
  - SecurityEvents
  connectorId: WindowsSecurityEvents
- dataTypes:
  - WindowsEvent
  connectorId: WindowsForwardedEvents

ARM

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2023-02-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/ca67c83e-7fff-4127-a3e3-1af66d6d4cad')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/ca67c83e-7fff-4127-a3e3-1af66d6d4cad')]",
      "properties": {
        "alertRuleTemplateName": "ca67c83e-7fff-4127-a3e3-1af66d6d4cad",
        "customDetails": null,
        "description": "'Identifies instances of a base64-encoded PE file header seen in the process command line parameter.'\n",
        "displayName": "Base64 encoded Windows process command-lines",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "Account",
                "identifier": "Name"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "Computer",
                "identifier": "FullName"
              },
              {
                "columnName": "HostName",
                "identifier": "HostName"
              },
              {
                "columnName": "DnsDomain",
                "identifier": "DnsDomain"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Endpoint Threat Protection Essentials/Analytic Rules/base64_encoded_pefile.yaml",
        "query": "let ProcessCreationEvents=(union isfuzzy=true\n(SecurityEvent\n| where EventID==4688\n| where isnotempty(CommandLine)\n| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,\nFileName = Process, CommandLine, ParentProcessName\n),\n(WindowsEvent\n| where EventID==4688\n| where EventData has \"TVqQAAMAAAAEAAA\"\n| extend CommandLine = tostring(EventData.CommandLine)\n| where isnotempty(CommandLine)\n| extend ParentProcessName = tostring(EventData.ParentProcessName)\n| extend NewProcessName = tostring(EventData.NewProcessName)\n| extend Process=tostring(split(NewProcessName, '\\\\')[-1])\n| extend SubjectUserName = tostring(EventData.SubjectUserName)\n| extend SubjectDomainName = tostring(EventData.SubjectDomainName)\n| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), count() by Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName,\nFileName = Process, CommandLine, ParentProcessName));\nProcessCreationEvents\n| where CommandLine contains \"TVqQAAMAAAAEAAA\"\n| extend HostName = iif(Computer has '.',substring(Computer,0,indexof(Computer,'.')),Computer) , DnsDomain = iif(Computer has '.',substring(Computer,indexof(Computer,'.')+1),'')\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "status": "Available",
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "DefenseEvasion",
          "Execution"
        ],
        "techniques": [
          "T1027",
          "T1059",
          "T1140"
        ],
        "templateVersion": "1.1.4",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}