WHOIS Expired Domain Executable Downloaded

/*
 * 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 whois_expired_domain_executable_downloaded {

  meta:
    author = "Google Cloud Security"
    description = "Detect web traffic to a recently expired domain followed by an exe file creation event"
    rule_id = "mr_ce0a1979-ec95-40d4-8107-748ee6d1e93f"
    rule_name = "WHOIS Expired Domain Executable Downloaded"
    type = "alert"
    tags = "whois"
    data_source = "zscalar, microsoft sysmon"
    platform = "Windows"
    severity = "Low"
    priority = "Low"

  events:
    $access.metadata.event_type = "NETWORK_HTTP"
    $access.principal.hostname = $hostname
    $access.target.hostname = $domain

    // join access event to entity graph to use WHOIS data
    $whois.graph.entity.domain.name = $domain

    // Whois domains provided by GCTI Feed
    $whois.graph.metadata.entity_type = "DOMAIN_NAME"
    $whois.graph.metadata.vendor_name = "WHOIS"
    $whois.graph.metadata.product_name = "WHOISXMLAPI Simple Whois"
    $whois.graph.metadata.source_type = "GLOBAL_CONTEXT"
    // Filter out domains without expiration time
    $whois.graph.entity.domain.expiration_time.seconds > 0
    // Domain expired before the event
    $whois.graph.entity.domain.expiration_time.seconds < $access.metadata.event_timestamp.seconds

    // join access event with executable file creation event by principal hostname
    $creation.principal.hostname = $hostname
    $creation.metadata.event_type = "FILE_CREATION"
    $creation.target.file.full_path = /\.exe/ nocase

    // file creation comes after network event
    $creation.metadata.event_timestamp.seconds > $access.metadata.event_timestamp.seconds

  match:
    $hostname over 1h

  outcome:
    $risk_score = 20
    // added to populate alert graph with additional context
    // Commented out principal.hostname because it is already represented in graph as match variable. If match changes, can uncomment to add to results
    //$principal_hostname = array_distinct($access.principal.hostname)
    $target_hostname = array_distinct($access.target.hostname)
    $principal_process_pid = array_distinct($access.principal.process.pid)
    $principal_process_command_line = array_distinct($access.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($access.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($access.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($access.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specific_process_id = array_distinct($access.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($access.target.process.pid)
    $target_process_command_line = array_distinct($access.target.process.command_line)
    $target_process_file_sha256 = array_distinct($access.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($access.target.process.file.full_path)
    $target_process_product_specific_process_id = array_distinct($access.target.process.product_specific_process_id)
    $target_process_parent_process_product_specific_process_id = array_distinct($access.target.process.parent_process.product_specific_process_id)
    $principal_user_userid = array_distinct($access.principal.user.userid)
    $target_user_userid = array_distinct($access.target.user.userid)
    $target_url = array_distinct($access.target.url)
    $target_file_sha256 = array_distinct($creation.target.file.sha256)
    $target_file_full_path = array_distinct($creation.target.file.full_path)

  condition:
    $access and $whois and $creation
}