Microsoft Sentinel Analytic Rules
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NRT Process executed from binary hidden in Base64 encoded file

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Id7ad4c32b-d0d2-411c-a0e8-b557afa12fce
RulenameNRT Process executed from binary hidden in Base64 encoded file
DescriptionEncoding malicious software is a technique used to obfuscate files from detection.

The first CommandLine component is looking for Python decoding base64.

The second CommandLine component is looking for Bash/sh command line base64 decoding.

The third one is looking for Ruby decoding base64.
SeverityMedium
TacticsExecution
DefenseEvasion
TechniquesT1059
T1027
T1140
Required data connectorsSecurityEvents
WindowsSecurityEvents
KindNRT
Source Urihttps://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Security Events/Analytic Rules/NRT_execute_base64_decodedpayload.yaml
Version1.0.2
Arm template7ad4c32b-d0d2-411c-a0e8-b557afa12fce.json
Deploy To Azure
SecurityEvent
| where EventID==4688
| where isnotempty(CommandLine)
| project TimeGenerated, Computer, AccountName = SubjectUserName, AccountNTDomain = SubjectDomainName, FileName = Process, CommandLine, ParentProcessName, SubjectAccount
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| where CommandLine contains ".decode('base64')"
        or CommandLine contains "base64 --decode"
        or CommandLine contains ".decode64("
id: 7ad4c32b-d0d2-411c-a0e8-b557afa12fce
name: NRT Process executed from binary hidden in Base64 encoded file
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: SubjectAccount
  - identifier: Name
    columnName: AccountName
  - identifier: NTDomain
    columnName: AccountNTDomain
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: Computer
  - identifier: HostName
    columnName: HostName
  - identifier: DnsDomain
    columnName: HostNameDomain
  entityType: Host
status: Available
query: |
  SecurityEvent
  | where EventID==4688
  | where isnotempty(CommandLine)
  | project TimeGenerated, Computer, AccountName = SubjectUserName, AccountNTDomain = SubjectDomainName, FileName = Process, CommandLine, ParentProcessName, SubjectAccount
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | where CommandLine contains ".decode('base64')"
          or CommandLine contains "base64 --decode"
          or CommandLine contains ".decode64("  
requiredDataConnectors:
- connectorId: SecurityEvents
  dataTypes:
  - SecurityEvent
- connectorId: WindowsSecurityEvents
  dataTypes:
  - SecurityEvent
severity: Medium
relevantTechniques:
- T1059
- T1027
- T1140
version: 1.0.2
kind: NRT
tactics:
- Execution
- DefenseEvasion
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Security Events/Analytic Rules/NRT_execute_base64_decodedpayload.yaml
description: |
  'Encoding malicious software is a technique used to obfuscate files from detection.
  The first CommandLine component is looking for Python decoding base64.
  The second CommandLine component is looking for Bash/sh command line base64 decoding.
  The third one is looking for Ruby decoding base64.'  
{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2024-01-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/7ad4c32b-d0d2-411c-a0e8-b557afa12fce')]",
      "kind": "NRT",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/7ad4c32b-d0d2-411c-a0e8-b557afa12fce')]",
      "properties": {
        "alertRuleTemplateName": "7ad4c32b-d0d2-411c-a0e8-b557afa12fce",
        "customDetails": null,
        "description": "'Encoding malicious software is a technique used to obfuscate files from detection.\nThe first CommandLine component is looking for Python decoding base64.\nThe second CommandLine component is looking for Bash/sh command line base64 decoding.\nThe third one is looking for Ruby decoding base64.'\n",
        "displayName": "NRT Process executed from binary hidden in Base64 encoded file",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SubjectAccount",
                "identifier": "FullName"
              },
              {
                "columnName": "AccountName",
                "identifier": "Name"
              },
              {
                "columnName": "AccountNTDomain",
                "identifier": "NTDomain"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "Computer",
                "identifier": "FullName"
              },
              {
                "columnName": "HostName",
                "identifier": "HostName"
              },
              {
                "columnName": "HostNameDomain",
                "identifier": "DnsDomain"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Security Events/Analytic Rules/NRT_execute_base64_decodedpayload.yaml",
        "query": "SecurityEvent\n| where EventID==4688\n| where isnotempty(CommandLine)\n| project TimeGenerated, Computer, AccountName = SubjectUserName, AccountNTDomain = SubjectDomainName, FileName = Process, CommandLine, ParentProcessName, SubjectAccount\n| extend HostName = tostring(split(Computer, \".\")[0]), DomainIndex = toint(indexof(Computer, '.'))\n| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)\n| where CommandLine contains \".decode('base64')\"\n        or CommandLine contains \"base64 --decode\"\n        or CommandLine contains \".decode64(\"\n",
        "severity": "Medium",
        "status": "Available",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "DefenseEvasion",
          "Execution"
        ],
        "techniques": [
          "T1027",
          "T1059",
          "T1140"
        ],
        "templateVersion": "1.0.2"
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}