New RUN Key Pointing to Suspicious Folder

/*
 * Copyright 2025 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 new_run_key_pointing_to_suspicious_folder {

  meta:
    author = "Florian Roth (Nextron Systems), Markus Neis, Sander Wiebing, Swachchhanda Shrawan Poudel (Nextron Systems)"
    description = "Detects suspicious new RUN key element pointing to an executable in a suspicious folder"
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_susp_run_key_img_folder.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "New RUN Key Pointing to Suspicious Folder"
    rule_id = "mr_ffc6cf7a-3eaf-4ca1-8dba-9a2d466f2a3a"
    sigma_uuid = "02ee49e2-e294-4d0f-9278-f5b3212fc588"
    sigma_status = "experimental"
    tactic = "TA0005"
    technique = "T1547.001"
    type = "Detection"
    data_source = "Sysmon"
    platform = "Windows"
    severity = "High"
    priority = "High"
    false_positives = "Software using weird folders for updates"

  events:
    $reg.metadata.event_type = "REGISTRY_MODIFICATION"
    (
        strings.contains(strings.to_lower($reg.target.registry.registry_key), "\\software\\microsoft\\windows\\currentversion\\run") or
        strings.contains(strings.to_lower($reg.target.registry.registry_key), "\\software\\wow6432node\\microsoft\\windows\\currentversion\\run") or
        strings.contains(strings.to_lower($reg.target.registry.registry_key), "\\software\\microsoft\\windows\\currentversion\\policies\\explorer\\run")
    )
    and
    (
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\perflogs") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\programdata") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\windows\\temp") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\temp") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\appdata\\local\\temp") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\appdata\\roaming") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\$recycle.bin") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\users\\default") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\users\\public") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "%temp%") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "%tmp%") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "%public%") or
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "%appdata%") or
        (
            strings.contains(strings.to_lower($reg.target.registry.registry_value_data), ":\\users\\") and
            (
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\favorites") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\favourites") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\contacts") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\music") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\pictures") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\documents") or
                strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\photos")
            )
        )
    )
    not (
        strings.contains(strings.to_lower($reg.target.registry.registry_key), "\\microsoft\\windows\\currentversion\\runonce\\") and
        strings.starts_with(strings.to_lower($reg.principal.process.file.full_path), "c:\\windows\\softwaredistribution\\download\\") and
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "rundll32.exe ") and
        strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "c:\\windows\\system32\\advpack.dll,delnoderundll32") and
        (
            strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "\\appdata\\local\\temp\\") or
            strings.contains(strings.to_lower($reg.target.registry.registry_value_data), "c:\\windows\\temp\\")
        )
    )

    $reg.principal.hostname = $hostname

  match:
    $hostname over 5m

  outcome:
    //example usage of specifying test user and hostname to adjust risk score
    $risk_score = max(if($reg.principal.user.userid = "user" and $reg.principal.hostname = "hostname", 0, 15))
    $principal_hostname = array_distinct($reg.principal.hostname)
    $principal_process_pid = array_distinct($reg.principal.process.pid)
    $principal_process_file_full_path = array_distinct($reg.principal.process.file.full_path)
    $principal_process_product_specific_process_id = array_distinct($reg.principal.process.product_specific_process_id)
    $principal_user_userid = array_distinct($reg.principal.user.userid)
    $target_registry_key = array_distinct($reg.target.registry.registry_key)
    $target_registry_value_data = array_distinct($reg.target.registry.registry_value_data)
    $log_type = array_distinct(strings.concat($reg.metadata.log_type,"/",$reg.metadata.product_event_type))

  condition:
    $reg
}