Multiple failed unique file downloads from OneDrive observed in the Microsoft Graph API

// Copyright 2025 Google LLC. Licensed under Apache-2.0.

rule ms_graph_failed_file_downloads_uniq_docs {

  meta:
    author = "Google Cloud Security"
    description = "This detects when a 401 Unauthorized status code is returned when attempting to download multiple unique files from OneDrive and may indicate a permissions issue for the user."
    rule_id = "mr_63f3d1b6-6d0c-4d35-8faf-2876aeb5c2e7"
    rule_name = "Multiple failed unique file downloads from OneDrive observed in the Microsoft Graph API"
    type = "alert"
    data_source = "MS Graph Activity Logs"
    platform = "Azure"
    severity = "Low"
    priority = "Low"

  events:
    $api.metadata.event_type = "NETWORK_HTTP"
    $api.metadata.product_event_type = "Microsoft Graph Activity"
    re.regex($api.target.url, `^https://graph\.microsoft\.com/v1\.0/drives/.*/content$`) nocase
    //Can be tuned for specific User Agent strings being used - by default GraphRunner does not forge the UA for this action
    //$api.network.http.user_agent = /PowerShell/ nocase
    $api.network.http.method = "GET"
    $api.network.http.response_code = 401
    $api.principal.ip = $ip
    $api.network.session_id = $session

  match:
    $ip, $session over 15m

  outcome:
    $risk_score = 35
    $event_count = count_distinct($api.metadata.id)
    $doc_count = count_distinct($api.target.url)
    $requesting_user_guid = array_distinct($api.principal.user.userid)
    $requesting_ip = array_distinct($api.principal.ip)
    $user_agent = array_distinct($api.network.http.user_agent)
    $location = array_distinct($api.principal.location.name)
    $target_application_id_guid = array_distinct($api.target.resource.product_object_id)
    $session_id = array_distinct($api.network.session_id)
    $target_url = array_distinct($api.target.url)

  condition:
    //Threshold on unique docs can be modified here
    $api and $doc_count > 2
}