Default RDP Port Changed to Non Standard Port

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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.
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 *     https://www.apache.org/licenses/LICENSE-2.0
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rule default_rdp_port_changed_to_non_standard_port {

  meta:
    author = "frack113"
    description = "Detects changes to the default RDP port. Remote desktop is a common feature in operating systems. It allows a user to log into a remote system using an interactive session with a graphical user interface. Microsoft refers to its implementation of the Remote Desktop Protocol (RDP) as Remote Desktop Services (RDS)."
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_change_rdp_port.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "Default RDP Port Changed to Non Standard Port"
    rule_id = "mr_13e82052-08dc-4475-b0df-d22fc689e4c8"
    sigma_uuid = "509e84b9-a71a-40e0-834f-05470369bd1e"
    sigma_status = "test"
    tactic = "TA0003"
    technique = "T1547.010"
    type = "Detection"
    data_source = "Sysmon"
    platform = "Windows"
    severity = "High"
    priority = "High"
    false_positives = "Unknown"

  events:
    $reg.metadata.event_type = "REGISTRY_MODIFICATION"
    re.regex($reg.target.registry.registry_key, `\\control\\terminal server\\winstations\\rdp-tcp\\portnumber$`) nocase
    NOT $reg.target.registry.registry_value_data  = "DWORD (0x00000d3d)" //3389

    $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
}