Entra ID application enumeration observed in the Microsoft Graph API

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rule ms_graph_enumerate_applications {

  meta:
    author = "Google Cloud Security"
    description = "Identify the use GraphRunner's Invoke-DumpApps function to collect applications and external apps as well as users that consented to permissions in their apps."
    rule_id = "mr_3715d986-b1a9-4bb2-b625-acc54cd5322d"
    rule_name = "Entra ID application enumeration observed in the Microsoft Graph API"
    assumption = "While additional API endpoints are called in the function, this rule is stripped down to the applications and servicePrincipals endpoint recursively requesting the appRole assigned to."
    reference = "https://github.com/dafthack/GraphRunner/blob/main/GraphRunner.ps1"
    type = "Alert"
    data_source = "MS Graph Activity Logs"
    platform = "Azure"
    severity = "Low"
    priority = "Low"

  events:
    $app_api.metadata.event_type = "NETWORK_HTTP"
    $app_api.metadata.product_event_type = "Microsoft Graph Activity"
    $app_api.target.url = "https://graph.microsoft.com/v1.0/applications" nocase
    $app_api.network.http.method = "GET"
    $app_api.network.http.response_code = 200
    //Can be tuned for specific User Agent strings being used - by default GraphRunner does not forge the UA for this action
    //$app_api.network.http.user_agent = /PowerShell/ nocase
    $app_api.principal.ip = $ip
    $app_api.network.session_id = $session

    $app_api.metadata.event_timestamp.seconds < $role_api.metadata.event_timestamp.seconds

    $role_api.metadata.event_type = "NETWORK_HTTP"
    $role_api.metadata.product_event_type = "Microsoft Graph Activity"
    re.regex($role_api.target.url, `^https:\/\/graph.microsoft.com\/v1.0\/servicePrincipals\(appId='.*'\)/appRoleAssignedTo$`) nocase
    $role_api.network.http.method = "GET"
    $role_api.network.http.response_code = 200
    //Can be tuned for specific User Agent strings being used - by default GraphRunner does not forge the UA for this action
    //$role_api.network.http.user_agent = /PowerShell/ nocase
    $role_api.principal.ip = $ip
    $role_api.network.session_id = $session
    re.capture($role_api.target.url, `^https:\/\/graph.microsoft.com\/v1.0\/servicePrincipals\(appId='(.*)'\)/appRoleAssignedTo$`) = $app_guid

  match:
    $ip, $session over 5m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($app_api.metadata.id) + count_distinct($role_api.metadata.id)
    $requesting_user_guid = array_distinct($app_api.principal.user.userid)
    $requesting_ip = array_distinct($app_api.principal.ip)
    $user_agent = array_distinct($app_api.network.http.user_agent)
    $location = array_distinct($app_api.principal.location.name)
    $target_application_id_guid = array_distinct($app_api.target.resource.product_object_id)
    $session_id = array_distinct($app_api.network.session_id)
    $application_count = count_distinct($app_guid)
    $application_list = array_distinct($app_guid) //limited to 25 applications

  condition:
    $app_api and $role_api
}