IOC SHA256 Hash VT

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 * 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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 * 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.
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rule ioc_sha256_hash_vt {

  meta:
    author = "Google Cloud Security"
    description = "Detect file/process events with watchlisted hashes from MISP that VT flagged as MS Office docx file types"
    rule_id = "mr_d36dec67-3af0-4d52-be78-1fe14c865006"
    rule_name = "IOC SHA256 Hash VT"
    type = "alert"
    tags = "threat indicators, vt enrichment"
    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 = "Medium"
    priority = "Medium"

  events:
    $process.metadata.event_type = "PROCESS_LAUNCH" or $process.metadata.event_type ="FILE_CREATION"
    $process.principal.hostname = $hostname
    $process.target.file.sha256 != ""
    $process.target.file.sha256 = $sha256
    // Enriched field from VirusTotal integration, can be commented out or modified if not using
    $process.target.file.file_type = "FILE_TYPE_DOCX"

    // 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 = "FILE"
    $ioc.graph.metadata.source_type = "ENTITY_CONTEXT"
    $ioc.graph.entity.file.sha256 = $sha256

  match:
    $hostname over 15m

  outcome:
    $risk_score = 65
    $event_count = count_distinct($process.metadata.id)
    // 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
    //$principal_hostname = array_distinct($process.principal.hostname)
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specific_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specific_process_id = array_distinct($process.target.process.product_specific_process_id)
    $principal_user_userid = array_distinct($process.principal.user.userid)
    $target_file_sha256 = array_distinct($process.target.file.sha256)
    $target_file_full_path = array_distinct($process.target.file.full_path)

  condition:
    $process and $ioc
}