O365 Login Activity To Uncommon Microsoft Cloud Apps

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rule o365_login_activity_to_uncommon_mscloud_apps {

  meta:
    author = "Google Cloud Security"
    description = "This rule detects O365 login activity to apps other than a defined list of first party MS Cloud Apps. Note that Azure Active Directory PowerShell and custom Azure apps are not in this list by default"
    rule_id = "mr_eca0cd3d-7d65-47f6-9df2-1a16664819ae"
    rule_name = "O365 Login Activity To Uncommon Microsoft Cloud Apps"
    assumption = "The list first_party_ms_cloud_apps is populated as needed"
    tactic = "TA0001"
    technique = "T1078.004"
    reference = "https://learn.microsoft.com/en-us/troubleshoot/azure/active-directory/verify-first-party-apps-sign-in"
    type = "alert"
    platform = "azure"
    data_source = "o365"
    severity = "Medium"
    priority = "Medium"

  events:
    $login.metadata.event_type = "USER_LOGIN"
    $login.metadata.product_event_type = "UserLoggedIn"
    $login.metadata.product_name = "Office 365"
    NOT $login.target.resource.product_object_id in %first_party_ms_cloud_apps
    /* Additional AppIds that are not in this list but have appeared benign during testing include the following:
    7eadcef8-456d-4611-9480-4fff72b8b9e2 Microsoft Account Controls V2
    8e0e8db5-b713-4e91-98e6-470fed0aa4c2 Microsoft Azure Signup Portal
    f9818e52-50bd-463e-8932-a1650bd3fad2 MSAL Configuration
    There are additional lists on GitHub that are compiled that would be added for additional tuning as needed
    */
    $login.metadata.vendor_name = "Microsoft"
    $login.security_result.action = "ALLOW"
    $login.target.user.userid = $userid

    //If you are using ADFS, you may want to consider something like this to filter out Synchronization Login Traffic - Your userid will be different
    $login.target.user.userid != /Sync_/ nocase

  match:
    $userid over 5m

  outcome:
    $risk_score = 65
    $event_count = count_distinct($login.metadata.id)
    $target_application = array_distinct($login.target.resource.product_object_id)
    $security_summary = array_distinct($login.security_result.summary)
    $user_agent = array_distinct($login.network.http.user_agent)
    $country_region_login_attempt = array_distinct($login.principal.ip_geo_artifact.location.country_or_region)
    //added to populate alert graph with additional context
    $principal_ip = array_distinct($login.principal.ip)
    $target_user_userid = array_distinct($login.target.user.userid)

  condition:
    $login
}