Suspicious Sign In by Entra ID Connect Sync Account

BehaviorAnalytics
// User modification is expected from this account so focus on logons
| where ActivityType =~ "LogOn"
| where UserName startswith "Sync_" and UsersInsights.AccountDisplayName =~ "On-Premises Directory Synchronization Service Account"
// Filter out this expected activity
| where ActivityInsights.App !~ "Microsoft Azure Active Directory Connect"
| where InvestigationPriority > 0
| extend Name = split(UserPrincipalName, "@")[0], UPNSuffix = split(UserPrincipalName, "@")[1]

triggerOperator: gt
queryFrequency: 1h
description: |
  'This query looks for sign ins by the Microsoft Entra ID Connect Sync account to Azure where properties about the logon are anomalous.
  This query uses Microsoft Sentinel's UEBA features to detect these suspicious properties.
  A threat actor may attempt to steal the Sync account credentials and use them to access Azure resources. This alert should be 
  reviewed to ensure that the log in came was from a legitimate source.'  
status: Available
kind: Scheduled
triggerThreshold: 0
requiredDataConnectors:
- connectorId: BehaviorAnalytics
  dataTypes:
  - BehaviorAnalytics
version: 1.0.3
queryPeriod: 1h
name: Suspicious Sign In by Entra ID Connect Sync Account
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/BehaviorAnalytics/SuspiciousSigninByAADConnectAccount.yaml
id: 2cd8b3d5-c9e0-4be3-80f7-0469d511c3f6
alertDetailsOverride:
  alertDescriptionFormat: |
    This query looks for sign ins by the Azure AD Connect Sync account to Azure where properties about the logon are anomalous.
    This query uses Microsoft Sentinel's UEBA features to detect these suspicious properties.
    A threat actor may attempt to steal the Sync account credentials and use them to access Azure resources. This alert should be 
    reviewed to ensure that the log in came was from a legitimate source.
    In this case {{UserPrincipalName}} logged in from {{SourceIPAddress}}.    
  alertDisplayNameFormat: Suspicious Sign In by AAD Connect Sync Account {{UserPrincipalName}} from {{SourceIPAddress}}
tactics:
- InitialAccess
metadata:
  source:
    kind: Community
  author:
    name: Microsoft Security Community
  categories:
    domains:
    - Identity
    - Security - Threat Protection
  support:
    tier: Community
relevantTechniques:
- T1078.004
severity: Medium
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: UserPrincipalName
  - identifier: Name
    columnName: Name
  - identifier: UPNSuffix
    columnName: UPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: SourceIPAddress
  entityType: IP
- fieldMappings:
  - identifier: HostName
    columnName: DestinationDevice
  entityType: Host
query: |
  BehaviorAnalytics
  // User modification is expected from this account so focus on logons
  | where ActivityType =~ "LogOn"
  | where UserName startswith "Sync_" and UsersInsights.AccountDisplayName =~ "On-Premises Directory Synchronization Service Account"
  // Filter out this expected activity
  | where ActivityInsights.App !~ "Microsoft Azure Active Directory Connect"
  | where InvestigationPriority > 0
  | extend Name = split(UserPrincipalName, "@")[0], UPNSuffix = split(UserPrincipalName, "@")[1]  

{
  "$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/2cd8b3d5-c9e0-4be3-80f7-0469d511c3f6')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/2cd8b3d5-c9e0-4be3-80f7-0469d511c3f6')]",
      "properties": {
        "alertDetailsOverride": {
          "alertDescriptionFormat": "This query looks for sign ins by the Azure AD Connect Sync account to Azure where properties about the logon are anomalous.\nThis query uses Microsoft Sentinel's UEBA features to detect these suspicious properties.\nA threat actor may attempt to steal the Sync account credentials and use them to access Azure resources. This alert should be \nreviewed to ensure that the log in came was from a legitimate source.\nIn this case {{UserPrincipalName}} logged in from {{SourceIPAddress}}.\n",
          "alertDisplayNameFormat": "Suspicious Sign In by AAD Connect Sync Account {{UserPrincipalName}} from {{SourceIPAddress}}"
        },
        "alertRuleTemplateName": "2cd8b3d5-c9e0-4be3-80f7-0469d511c3f6",
        "customDetails": null,
        "description": "'This query looks for sign ins by the Microsoft Entra ID Connect Sync account to Azure where properties about the logon are anomalous.\nThis query uses Microsoft Sentinel's UEBA features to detect these suspicious properties.\nA threat actor may attempt to steal the Sync account credentials and use them to access Azure resources. This alert should be \nreviewed to ensure that the log in came was from a legitimate source.'\n",
        "displayName": "Suspicious Sign In by Entra ID Connect Sync Account",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "UserPrincipalName",
                "identifier": "FullName"
              },
              {
                "columnName": "Name",
                "identifier": "Name"
              },
              {
                "columnName": "UPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "SourceIPAddress",
                "identifier": "Address"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "DestinationDevice",
                "identifier": "HostName"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/BehaviorAnalytics/SuspiciousSigninByAADConnectAccount.yaml",
        "query": "BehaviorAnalytics\n// User modification is expected from this account so focus on logons\n| where ActivityType =~ \"LogOn\"\n| where UserName startswith \"Sync_\" and UsersInsights.AccountDisplayName =~ \"On-Premises Directory Synchronization Service Account\"\n// Filter out this expected activity\n| where ActivityInsights.App !~ \"Microsoft Azure Active Directory Connect\"\n| where InvestigationPriority > 0\n| extend Name = split(UserPrincipalName, \"@\")[0], UPNSuffix = split(UserPrincipalName, \"@\")[1]\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT1H",
        "severity": "Medium",
        "status": "Available",
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "InitialAccess"
        ],
        "techniques": [
          "T1078"
        ],
        "templateVersion": "1.0.3",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}