Exchange OAB Virtual Directory Attribute Containing Potential Webshell

SecurityEvent
// Look for specific Directory Service Changes and parse data
| where EventID == 5136
| extend EventData = parse_xml(EventData).EventData.Data
| mv-expand bagexpansion = array EventData
| evaluate bag_unpack(EventData)
| extend Key = tostring(column_ifexists('@Name', "")), Value = column_ifexists('#text', "")
| evaluate pivot(Key, any(Value),TimeGenerated, EventID, Computer, Account, AccountType, EventSourceName, Activity, SubjectAccount)
// Where changes relate to Exchange OAB
| extend ObjectClass = column_ifexists("ObjectClass", "")
| where ObjectClass =~ "msExchOABVirtualDirectory"
// Look for InternalHostName or ExternalHostName properties being changed
| extend AttributeLDAPDisplayName = column_ifexists("AttributeLDAPDisplayName", "")
| where AttributeLDAPDisplayName in~ ("msExchExternalHostName", "msExchInternalHostName")
// Look for suspected webshell activity
| extend AttributeValue = column_ifexists("AttributeValue", "")
| where AttributeValue has "script"
| project-rename LastSeen = TimeGenerated
| extend ObjectDN = column_ifexists("ObjectDN", "")
| project-reorder LastSeen, Computer, Account, ObjectDN, AttributeLDAPDisplayName, AttributeValue
| extend timestamp = LastSeen, AccountCustomEntity = Account, HostCustomEntity = Computer

triggerOperator: gt
version: 1.0.2
query: |
  SecurityEvent
  // Look for specific Directory Service Changes and parse data
  | where EventID == 5136
  | extend EventData = parse_xml(EventData).EventData.Data
  | mv-expand bagexpansion = array EventData
  | evaluate bag_unpack(EventData)
  | extend Key = tostring(column_ifexists('@Name', "")), Value = column_ifexists('#text', "")
  | evaluate pivot(Key, any(Value),TimeGenerated, EventID, Computer, Account, AccountType, EventSourceName, Activity, SubjectAccount)
  // Where changes relate to Exchange OAB
  | extend ObjectClass = column_ifexists("ObjectClass", "")
  | where ObjectClass =~ "msExchOABVirtualDirectory"
  // Look for InternalHostName or ExternalHostName properties being changed
  | extend AttributeLDAPDisplayName = column_ifexists("AttributeLDAPDisplayName", "")
  | where AttributeLDAPDisplayName in~ ("msExchExternalHostName", "msExchInternalHostName")
  // Look for suspected webshell activity
  | extend AttributeValue = column_ifexists("AttributeValue", "")
  | where AttributeValue has "script"
  | project-rename LastSeen = TimeGenerated
  | extend ObjectDN = column_ifexists("ObjectDN", "")
  | project-reorder LastSeen, Computer, Account, ObjectDN, AttributeLDAPDisplayName, AttributeValue
  | extend timestamp = LastSeen, AccountCustomEntity = Account, HostCustomEntity = Computer  
status: Available
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: AccountCustomEntity
    identifier: FullName
- entityType: Host
  fieldMappings:
  - columnName: HostCustomEntity
    identifier: FullName
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Security Events/Analytic Rules/ExchangeOABVirtualDirectoryAttributeContainingPotentialWebshell.yaml
queryFrequency: 1h
requiredDataConnectors:
- connectorId: SecurityEvents
  dataTypes:
  - SecurityEvent
- connectorId: WindowsSecurityEvents
  dataTypes:
  - SecurityEvent
name: Exchange OAB Virtual Directory Attribute Containing Potential Webshell
queryPeriod: 1h
severity: High
kind: Scheduled
tactics:
- InitialAccess
id: faf1a6ff-53b5-4f92-8c55-4b20e9957594
description: |
  'This query uses Windows Event ID 5136 in order to detect potential webshell deployment by exploitation of CVE-2021-27065.
  This query looks for changes to the InternalHostName or ExternalHostName properties of Exchange OAB Virtual Directory objects in AD Directory Services
  where the new objects contain potential webshell objects.'  
relevantTechniques:
- T1190
triggerThreshold: 0

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/faf1a6ff-53b5-4f92-8c55-4b20e9957594')]",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/faf1a6ff-53b5-4f92-8c55-4b20e9957594')]",
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules",
      "kind": "Scheduled",
      "apiVersion": "2022-11-01-preview",
      "properties": {
        "displayName": "Exchange OAB Virtual Directory Attribute Containing Potential Webshell",
        "description": "'This query uses Windows Event ID 5136 in order to detect potential webshell deployment by exploitation of CVE-2021-27065.\nThis query looks for changes to the InternalHostName or ExternalHostName properties of Exchange OAB Virtual Directory objects in AD Directory Services\nwhere the new objects contain potential webshell objects.'\n",
        "severity": "High",
        "enabled": true,
        "query": "SecurityEvent\n// Look for specific Directory Service Changes and parse data\n| where EventID == 5136\n| extend EventData = parse_xml(EventData).EventData.Data\n| mv-expand bagexpansion = array EventData\n| evaluate bag_unpack(EventData)\n| extend Key = tostring(column_ifexists('@Name', \"\")), Value = column_ifexists('#text', \"\")\n| evaluate pivot(Key, any(Value),TimeGenerated, EventID, Computer, Account, AccountType, EventSourceName, Activity, SubjectAccount)\n// Where changes relate to Exchange OAB\n| extend ObjectClass = column_ifexists(\"ObjectClass\", \"\")\n| where ObjectClass =~ \"msExchOABVirtualDirectory\"\n// Look for InternalHostName or ExternalHostName properties being changed\n| extend AttributeLDAPDisplayName = column_ifexists(\"AttributeLDAPDisplayName\", \"\")\n| where AttributeLDAPDisplayName in~ (\"msExchExternalHostName\", \"msExchInternalHostName\")\n// Look for suspected webshell activity\n| extend AttributeValue = column_ifexists(\"AttributeValue\", \"\")\n| where AttributeValue has \"script\"\n| project-rename LastSeen = TimeGenerated\n| extend ObjectDN = column_ifexists(\"ObjectDN\", \"\")\n| project-reorder LastSeen, Computer, Account, ObjectDN, AttributeLDAPDisplayName, AttributeValue\n| extend timestamp = LastSeen, AccountCustomEntity = Account, HostCustomEntity = Computer\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT1H",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0,
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1190"
        ],
        "alertRuleTemplateName": "faf1a6ff-53b5-4f92-8c55-4b20e9957594",
        "customDetails": null,
        "entityMappings": [
          {
            "fieldMappings": [
              {
                "columnName": "AccountCustomEntity",
                "identifier": "FullName"
              }
            ],
            "entityType": "Account"
          },
          {
            "fieldMappings": [
              {
                "columnName": "HostCustomEntity",
                "identifier": "FullName"
              }
            ],
            "entityType": "Host"
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Windows Security Events/Analytic Rules/ExchangeOABVirtualDirectoryAttributeContainingPotentialWebshell.yaml",
        "status": "Available",
        "templateVersion": "1.0.2"
      }
    }
  ]
}