IOC Domain C2

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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
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 * 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 ioc_domain_C2 {

  meta:
    author = "Google Cloud Security"
    description = "Detect DNS events that indicate communication to a C2 domain in MISP"
    rule_id = "mr_cb22c45e-b29d-487f-9cf5-1310bfed6d6c"
    rule_name = "IOC Domain C2"
    type = "alert"
    tags = "threat indicators"
    assumption = "Assumes MISP data has been ingested into entity graph; this rule can be modified to utilize other TI indicators"
    data_source = "microsoft sysmon"
    severity = "High"
    priority = "High"

  events:
    $dns.metadata.event_type = "NETWORK_DNS"
    $dns.network.dns.questions.name = $dns_query

    // Correlates with MISP data; can be modified based on your MISP parser or other TI
    $ioc.graph.metadata.product_name = "MISP"
    $ioc.graph.metadata.entity_type = "DOMAIN_NAME"
    $ioc.graph.metadata.source_type = "ENTITY_CONTEXT"
    //Summary is used to focus on a specific subset of MISP indicators, can modify as needed
    $ioc.graph.metadata.threat.summary = "C2 domains"
    $ioc.graph.entity.hostname = $dns_query

  match:
    $dns_query over 5m

  outcome:
    $risk_score = 85
    $event_count = count_distinct($dns.metadata.id)
    $network_dns_questions_name = array_distinct($dns.network.dns.questions.name)
    $network_dns_answers_data = array_distinct($dns.network.dns.answers.data)
    // added to populate alert graph with additional context
    $principal_ip = array_distinct($dns.principal.ip)
    $target_ip = array_distinct($dns.target.ip)
    $principal_process_pid = array_distinct($dns.principal.process.pid)
    $principal_process_file_full_path = array_distinct($dns.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($dns.principal.process.product_specific_process_id)
    $principal_user_userid = array_distinct($dns.principal.user.userid)
    $principal_process_command_line = array_distinct($dns.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($dns.principal.process.file.sha256)
    $principal_process_parent_process_product_specific_process_id = array_distinct($dns.principal.process.parent_process.product_specific_process_id)


  condition:
    $dns and $ioc
}