RestrictedAdminMode Registry Value Tampering

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 * 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 restrictedadminmode_registry_value_tampering {

  meta:
    author = "frack113"
    description = "Detects changes to the \"DisableRestrictedAdmin\" registry value in order to disable or enable RestrictedAdmin mode.\nRestrictedAdmin mode prevents the transmission of reusable credentials to the remote system to which you connect using Remote Desktop.\nThis prevents your credentials from being harvested during the initial connection process if the remote server has been compromise"
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_lsa_disablerestrictedadmin.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "RestrictedAdminMode Registry Value Tampering"
    rule_id = "mr_c996dba7-ebc0-4472-849c-d6ddebffa601"
    sigma_uuid = "d6ce7ebd-260b-4323-9768-a9631c8d4db2"
    sigma_status = "test"
    tactic = "TA0005"
    technique = "T1112"
    type = "Detection"
    data_source = "Sysmon Windows Registry"
    platform = "Windows"
    severity = "High"
    priority = "High"
    false_positives = "Unknown"

  events:
    $reg.metadata.event_type = "REGISTRY_MODIFICATION"
    re.regex($reg.target.registry.registry_key, `System\\CurrentControlSet\\Control\\Lsa\\DisableRestrictedAdmin$`) nocase

    $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
}