Guest Users Invited to Tenant by New Inviters | Microsoft Sentinel Analytic Rules

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Id	572e75ef-5147-49d9-9d65-13f2ed1e3a86
Rulename	Guest Users Invited to Tenant by New Inviters
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
Severity	Medium
Tactics	Persistence
Techniques	T1078.004
Required data connectors	AzureActiveDirectory
Kind	Scheduled
Query frequency	1d
Query period	14d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/GuestUsersInvitedtoTenantbyNewInviters.yaml
Version	1.1.1
Arm template	572e75ef-5147-49d9-9d65-13f2ed1e3a86.json

KQL

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

YAML

relevantTechniques:
- T1078.004
tactics:
- Persistence
queryFrequency: 1d
metadata:
  author:
    name: Microsoft Security Research
  categories:
    domains:
    - Security - Others
    - Identity
  support:
    tier: Community
  source:
    kind: Community
queryPeriod: 14d
triggerThreshold: 0
name: Guest Users Invited to Tenant by New Inviters
kind: Scheduled
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
entityMappings:
- 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: Account
- fieldMappings:
  - columnName: InitiatingIPAddress
    identifier: Address
  entityType: IP
tags:
- AADSecOpsGuide
version: 1.1.1
requiredDataConnectors:
- dataTypes:
  - AuditLogs
  connectorId: AzureActiveDirectory
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/GuestUsersInvitedtoTenantbyNewInviters.yaml
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
severity: Medium
triggerOperator: gt

ARM

{
  "$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"
    }
  ]
}