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

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 * you may not use this file except in compliance with the License.
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rule ms_graph_failed_file_downloads_multiple_attempts {

  meta:
    author = "Google Cloud Security"
    description = "This detects when a 401 Unauthorized status is received on multiple attempts of the same file when attempting to download from OneDrive and may indicate a permissions issue for the user."
    rule_id = "mr_1117b547-0f30-444e-b10e-c9cfdf00f1f5"
    rule_name = "Multiple failed 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
    $api.target.url = $url

  match:
    $ip, $session, $url 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:
    //Tune to the desired threshold
    #api > 2
}