Google Safebrowsing File Contacts Tor Exit Node

/*
 * 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_safebrowsing_file_contacts_tor_exit_node {

  meta:
    author = "Google Cloud Security"
    description = "A malicious file contacting a known Tor Exit Node."
    rule_id = "mr_f6733319-50b3-477e-bad6-96bb4c14c632"
    rule_name = "Google Safebrowsing File Contacts Tor Exit Node"
    tactic = "TA0011"
    technique = "T1090.003"
    type = "alert"
    data_source = "microsoft defender atp, crowdstrike, microsoft sysmon"
    severity = "Critical"
    priority = "High"

  events:
    $network.metadata.event_type = "NETWORK_CONNECTION"
    $network.principal.process.file.sha256 != ""
    $network.principal.process.file.sha256 = $file_hash
    $network.principal.hostname = $hostname
    $network.target.ip = $ip

    // Safe Browsing file hashes provided by GCTI Feed
    $safebrowse.graph.metadata.product_name = "Google Safe Browsing"
    $safebrowse.graph.metadata.entity_type = "FILE"
    $safebrowse.graph.metadata.source_type = "GLOBAL_CONTEXT"
    $safebrowse.graph.metadata.threat.category = "SOFTWARE_MALICIOUS"
    $safebrowse.graph.entity.file.sha256 = $file_hash

    // Tor IP listing provided by GCTI Feed
    $gcti.graph.entity.artifact.ip = $ip
    $gcti.graph.metadata.entity_type = "IP_ADDRESS"
    $gcti.graph.metadata.source_type = "GLOBAL_CONTEXT"
    $gcti.graph.metadata.threat.threat_feed_name = "Tor Exit Nodes"
    $gcti.graph.metadata.vendor_name = "Google Cloud Threat Intelligence"
    $gcti.graph.metadata.product_name = "GCTI Feed"

  match:
    $hostname over 1h

  outcome:
    $risk_score = 95
    $event_count = count_distinct($network.metadata.id)
    //added to populate alert graph with additional context
    $principal_ip = array_distinct($network.principal.ip)
    $target_ip = array_distinct($network.target.ip)
    $principal_process_pid = array_distinct($network.principal.process.pid)
    $principal_process_command_line = array_distinct($network.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($network.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($network.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($network.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specific_process_id = array_distinct($network.principal.process.parent_process.product_specific_process_id)
    //$target_process_pid = array_distinct($network.target.process.pid)
    $target_process_command_line = array_distinct($network.target.process.command_line)
    $target_process_file_sha256 = array_distinct($network.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($network.target.process.file.full_path)
    $target_process_product_specific_process_id = array_distinct($network.target.process.product_specific_process_id)
    $target_process_parent_process_product_specific_process_id = array_distinct($network.target.process.parent_process.product_specific_process_id)
    $principal_user_userid = array_distinct($network.principal.user.userid)
    $target_user_userid = array_distinct($network.target.user.userid)

  condition:
    $network and $gcti and $safebrowse
}