Guest Users Invited to Tenant by New Inviters

id: 572e75ef-5147-49d9-9d65-13f2ed1e3a86
name: 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
requiredDataConnectors:
  - connectorId: AzureActiveDirectory
    dataTypes:
      - AuditLogs
queryFrequency: 1d
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Persistence
relevantTechniques:
  - T1078.004
tags:
  - AADSecOpsGuide
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
entityMappings:
  - entityType: Account
    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: IP
    fieldMappings:
      - identifier: Address
        columnName: InitiatingIPAddress
version: 1.1.1
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Microsoft Security Research
    support:
        tier: Community
    categories:
        domains: [ "Security - Others", "Identity" ]