Guest Users Invited to Tenant by New Inviters

let inviting_users = (AuditLogs
  | where TimeGenerated between(ago(14d)..ago(1d))
  | where OperationName =~ "Invite external user"
  | where Result =~ "success"
  | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
  | where isnotempty(InitiatingUserPrincipalName)
  | summarize by InitiatingUserPrincipalName);
  AuditLogs
  | where TimeGenerated > ago(1d)
  | where OperationName =~ "Invite external user"
  | where Result =~ "success"
  | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
  | extend InitiatingAadUserId = tostring(InitiatedBy.user.id)
  | extend InitiatingIPAddress = tostring(InitiatedBy.user.ipAddress)
  | where isnotempty(InitiatingUserPrincipalName) and InitiatingUserPrincipalName !in (inviting_users)
  | extend TargetUserPrincipalName = tostring(TargetResources[0].userPrincipalName)
  | extend TargetAadUserId = tostring(TargetResources[0].id)
  | extend invitingUser = InitiatingUserPrincipalName, invitedUserPrincipalName = TargetUserPrincipalName
  | extend InitiatingAccountName = tostring(split(InitiatingUserPrincipalName, "@")[0]), InitiatingAccountUPNSuffix = tostring(split(InitiatingUserPrincipalName, "@")[1])
  | extend TargetAccountName = tostring(split(TargetUserPrincipalName, "@")[0]), TargetAccountUPNSuffix = tostring(split(TargetUserPrincipalName, "@")[1])
  | project-reorder TimeGenerated, OperationName, Result, TargetUserPrincipalName, TargetAadUserId, InitiatingUserPrincipalName, InitiatingAadUserId, InitiatingIPAddress

name: Guest Users Invited to Tenant by New Inviters
triggerOperator: gt
query: |
  let inviting_users = (AuditLogs
    | where TimeGenerated between(ago(14d)..ago(1d))
    | where OperationName =~ "Invite external user"
    | where Result =~ "success"
    | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
    | where isnotempty(InitiatingUserPrincipalName)
    | summarize by InitiatingUserPrincipalName);
    AuditLogs
    | where TimeGenerated > ago(1d)
    | where OperationName =~ "Invite external user"
    | where Result =~ "success"
    | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
    | extend InitiatingAadUserId = tostring(InitiatedBy.user.id)
    | extend InitiatingIPAddress = tostring(InitiatedBy.user.ipAddress)
    | where isnotempty(InitiatingUserPrincipalName) and InitiatingUserPrincipalName !in (inviting_users)
    | extend TargetUserPrincipalName = tostring(TargetResources[0].userPrincipalName)
    | extend TargetAadUserId = tostring(TargetResources[0].id)
    | extend invitingUser = InitiatingUserPrincipalName, invitedUserPrincipalName = TargetUserPrincipalName
    | extend InitiatingAccountName = tostring(split(InitiatingUserPrincipalName, "@")[0]), InitiatingAccountUPNSuffix = tostring(split(InitiatingUserPrincipalName, "@")[1])
    | extend TargetAccountName = tostring(split(TargetUserPrincipalName, "@")[0]), TargetAccountUPNSuffix = tostring(split(TargetUserPrincipalName, "@")[1])
    | project-reorder TimeGenerated, OperationName, Result, TargetUserPrincipalName, TargetAadUserId, InitiatingUserPrincipalName, InitiatingAadUserId, InitiatingIPAddress
queryFrequency: 1d
description: |
  'Detects when a Guest User is added by a user account that has not been seen adding a guest in the previous 14 days.
    Monitoring guest accounts and the access they are provided is important to detect potential account abuse.
    Accounts added should be investigated to ensure the activity was legitimate.
    Ref: https://docs.microsoft.com/azure/active-directory/fundamentals/security-operations-user-accounts#monitoring-for-failed-unusual-sign-ins'
id: 572e75ef-5147-49d9-9d65-13f2ed1e3a86
triggerThreshold: 0
queryPeriod: 14d
version: 1.1.1
kind: Scheduled
relevantTechniques:
- T1078.004
tags:
- AADSecOpsGuide
severity: Medium
requiredDataConnectors:
- connectorId: AzureActiveDirectory
  dataTypes:
  - AuditLogs
metadata:
  categories:
    domains:
    - Security - Others
    - Identity
  support:
    tier: Community
  author:
    name: Microsoft Security Research
  source:
    kind: Community
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/GuestUsersInvitedtoTenantbyNewInviters.yaml
tactics:
- Persistence
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: InitiatingUserPrincipalName
  - identifier: Name
    columnName: InitiatingAccountName
  - identifier: UPNSuffix
    columnName: InitiatingAccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: TargetUserPrincipalName
  - identifier: Name
    columnName: TargetAccountName
  - identifier: UPNSuffix
    columnName: TargetAccountUPNSuffix
  entityType: Account
- fieldMappings:
  - identifier: AadUserId
    columnName: InitiatingAadUserId
  entityType: Account
- fieldMappings:
  - identifier: AadUserId
    columnName: TargetAadUserId
  entityType: Account
- fieldMappings:
  - identifier: Address
    columnName: InitiatingIPAddress
  entityType: IP

{
  "$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/572e75ef-5147-49d9-9d65-13f2ed1e3a86')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/572e75ef-5147-49d9-9d65-13f2ed1e3a86')]",
      "properties": {
        "alertRuleTemplateName": "572e75ef-5147-49d9-9d65-13f2ed1e3a86",
        "customDetails": null,
        "description": "'Detects when a Guest User is added by a user account that has not been seen adding a guest in the previous 14 days.\n  Monitoring guest accounts and the access they are provided is important to detect potential account abuse.\n  Accounts added should be investigated to ensure the activity was legitimate.\n  Ref: https://docs.microsoft.com/azure/active-directory/fundamentals/security-operations-user-accounts#monitoring-for-failed-unusual-sign-ins'\n",
        "displayName": "Guest Users Invited to Tenant by New Inviters",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "InitiatingUserPrincipalName",
                "identifier": "FullName"
              },
              {
                "columnName": "InitiatingAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "InitiatingAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "TargetUserPrincipalName",
                "identifier": "FullName"
              },
              {
                "columnName": "TargetAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "TargetAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "InitiatingAadUserId",
                "identifier": "AadUserId"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "TargetAadUserId",
                "identifier": "AadUserId"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "InitiatingIPAddress",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/GuestUsersInvitedtoTenantbyNewInviters.yaml",
        "query": "let inviting_users = (AuditLogs\n  | where TimeGenerated between(ago(14d)..ago(1d))\n  | where OperationName =~ \"Invite external user\"\n  | where Result =~ \"success\"\n  | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)\n  | where isnotempty(InitiatingUserPrincipalName)\n  | summarize by InitiatingUserPrincipalName);\n  AuditLogs\n  | where TimeGenerated > ago(1d)\n  | where OperationName =~ \"Invite external user\"\n  | where Result =~ \"success\"\n  | extend InitiatingUserPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)\n  | extend InitiatingAadUserId = tostring(InitiatedBy.user.id)\n  | extend InitiatingIPAddress = tostring(InitiatedBy.user.ipAddress)\n  | where isnotempty(InitiatingUserPrincipalName) and InitiatingUserPrincipalName !in (inviting_users)\n  | extend TargetUserPrincipalName = tostring(TargetResources[0].userPrincipalName)\n  | extend TargetAadUserId = tostring(TargetResources[0].id)\n  | extend invitingUser = InitiatingUserPrincipalName, invitedUserPrincipalName = TargetUserPrincipalName\n  | extend InitiatingAccountName = tostring(split(InitiatingUserPrincipalName, \"@\")[0]), InitiatingAccountUPNSuffix = tostring(split(InitiatingUserPrincipalName, \"@\")[1])\n  | extend TargetAccountName = tostring(split(TargetUserPrincipalName, \"@\")[0]), TargetAccountUPNSuffix = tostring(split(TargetUserPrincipalName, \"@\")[1])\n  | project-reorder TimeGenerated, OperationName, Result, TargetUserPrincipalName, TargetAadUserId, InitiatingUserPrincipalName, InitiatingAadUserId, InitiatingIPAddress\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P14D",
        "severity": "Medium",
        "subTechniques": [
          "T1078.004"
        ],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "Persistence"
        ],
        "tags": [
          "AADSecOpsGuide"
        ],
        "techniques": [
          "T1078"
        ],
        "templateVersion": "1.1.1",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}