Google Workspace Multiple Files Sent As Email Attachments From Google Drive

/*
 * Copyright 2023 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES 
OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule google_workspace_multiple_files_sent_as_email_attachment_from_google_drive {

  meta:
    author = "Google Cloud Security"
    description = "Identifies when a user sends multiple files from Google Drive as an email attachment to a free email domain, which may indicate data exfiltration."
    rule_id = "mr_125c517c-3ef9-4687-8af6-d71eff83d0e9"
    rule_name = "Google Workspace Multiple Files Sent As Email Attachments From Google Drive"
    mitre_attack_tactic = "Exfiltration"
    mitre_attack_technique = "Exfiltration Over Web Service"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1567/"
    mitre_attack_version = "v13.1"
    type = "Alert"
    data_source = "Workspace Activity"
    severity = "High"
    priority = "High"

  events:
    $email.metadata.vendor_name = "Google Workspace"
    $email.metadata.product_name = "drive"
    $email.metadata.event_type = "EMAIL_TRANSACTION"
    $email.metadata.product_event_type = "email_as_attachment"
    $email.target.user.email_addresses = /.*@gmail\.com
| .*@aol\.com
| .*@ymail\.com
| .*@ymail\.com
| .*@hotmail\.com
| .*@outlook\.com
| .*@icloud\.com/
    $email.principal.user.userid = $user_id

  match:
    $user_id over 1h

  outcome:
    $risk_score = max(75)
    $mitre_attack_tactic = "Exfiltration"
    $mitre_attack_technique = "Exfiltration Over Web Service"
    $mitre_attack_technique_id = "T1567"
    $event_count = count_distinct($email.metadata.id)
    $product_event_type = array_distinct($email.metadata.product_event_type)
    $userid = array_distinct($email.principal.user.userid)
    $doc_type = array_distinct($email.src.resource.attribute.labels["doc_type"])
    $owner = array_distinct($email.target.resource.attribute.labels["owner"])
    $target_emails = array_distinct($email.target.user.email_addresses)
    $doc_name = array_distinct($email.target.resource.name)
    $doc_id = array_distinct($email.target.resource.product_object_id)
    $count_docs = count_distinct($email.target.resource.product_object_id)

  condition:
    // Customize the value of $count_docs to set the alerting threshold for your environment
    $email and $count_docs > 10
}