O365 Entra ID Application Creation

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule o365_entra_id_application_creation {

  meta:
    author = "Google Cloud Security"
    description = "Application creation is a legitimate activity but doesn't occur frequently. Alerts when a new application is created in Entra ID (formerly Azure AD)."
    rule_id = "mr_c8daf9ab-2b39-46cc-bda9-7fd1ebb13a81"
    rule_name = "O365 Entra ID Application Creation"
    type = "alert"
    platform = "azure"
    data_source = "o365"
    severity = "Low"
    priority = "Medium"

  events:
    $app.metadata.event_type = "USER_RESOURCE_CREATION"
    $app.metadata.product_name = "Office 365"
    $app.metadata.vendor_name = "Microsoft"
    $app.metadata.product_event_type = "Add application."
    $app.security_result.action = "ALLOW"
    //These events should have a userid associated with them but in case they don't we will match on the app name being created instead
    strings.coalesce($app.principal.user.userid, $app.target.resource.name) = $user_or_resource

  match:
    $user_or_resource over 5m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($app.metadata.id)
    $target_application = array_distinct($app.target.application)
    $security_summary = array_distinct($app.security_result.summary)
    $user_agent = array_distinct($app.network.http.user_agent)
    //added to populate alert graph with additional context
    $principal_user_userid = array_distinct($app.principal.user.userid)
    $target_resource_name = array_distinct($app.target.resource.name)

  condition:
    $app
}