Windows Short Term Account Use

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 * 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 win_short_term_account_use {

  meta:
    author = "Google Cloud Security"
    description = "Detects the creation, login, and deletion of a user account over a predefined timeframe"
    rule_id = "mr_ac28ce76-8197-4354-af0d-d77c5771d9df"
    rule_name = "Windows Short Term Account Use"
    type = "alert"
    platform = "windows"
    data_source = "microsoft windows events"
    severity = "Medium"
    priority = "Medium"

  events:
    $create.metadata.event_type = "USER_CREATION"
    $create.target.user.userid = $targetUser

    $create.metadata.event_timestamp.seconds < $login.metadata.event_timestamp.seconds

    $login.metadata.event_type = "USER_LOGIN"
    //Focus is on Windows login events with this event code but could be modified for other platforms as well
    $login.metadata.product_event_type = "4624"
    $login.target.user.userid = $targetUser

    $login.metadata.event_timestamp.seconds < $delete.metadata.event_timestamp.seconds

    $delete.metadata.event_type = "USER_DELETION"
    $delete.target.user.userid = $targetUser

  match:
    $targetUser over 4h

  outcome:
    $risk_score = 65
    $event_count = count_distinct($login.metadata.id)
    // added to populate alert graph with additional context
    $principal_hostname = array_distinct($login.principal.hostname)
    $src_hostname = array_distinct($login.src.hostname)
    $src_ip = array_distinct($login.src.ip)
    $principal_user_userid = array_distinct($login.principal.user.userid)
    $principal_user_employee_id = array_distinct($login.principal.user.employee_id)
    // principal_process_id for each of the three types of events
    $user_creation_process_id = array_distinct($create.principal.process.pid)
    $user_login_process_id = array_distinct($login.principal.process.pid)
    $user_deletion_process_id = array_distinct($delete.principal.process.pid)
    $target_process_file_full_path = array_distinct($login.target.process.file.full_path)
    // Commented out target.user.userid because it is already represented in graph as match variable. If match changes, can uncomment to add to results
    //$target_user_userid = array_distinct($login.target.user.userid)
    $principal_resource_name = array_distinct($login.principal.resource.name)
    $target_resource_name = array_distinct($login.target.resource.name)
    $target_url = array_distinct($login.target.url)

  condition:
    $create and $login and $delete

}