huntrule

Windows: Outbound RDP (3389) Connections Initiated by Non-Standard Processes

Alerts on outbound port 3389 connections on Windows when initiated by an unapproved process, suggesting non-standard RDP tooling.

FreeReviewedSigma · High · v2
Product
windows
Category
network_connection
Author
Markus Neis (SigmaHQ), DRL 1.1
Published
2019-05-15
Updated
2026-07-31
AnalysisDetection
title: "Windows: Outbound RDP (3389) Connections Initiated by Non-Standard Processes"
id: 875dd0c7-e882-4463-88c1-3ea4790de906
status: test
description: This rule identifies outbound network connections to destination port 3389 that are initiated by processes other than the expected mstsc.exe RDP client and other commonly allowed RDP-related binaries. Attackers may use alternate tools to establish RDP sessions for lateral movement while avoiding detection tied to mstsc.exe. The rule relies on Windows network connection telemetry with fields for destination port, initiation status, and the initiating process image path (including image exceptions).
references:
  - https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-0708
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/network_connection/net_connection_win_rdp_outbound_over_non_standard_tools.yml
author: Markus Neis, Huntrule Team
date: 2019-05-15
modified: 2024-02-09
tags:
  - attack.lateral-movement
  - attack.t1021.001
  - car.2013-07-002
logsource:
  category: network_connection
  product: windows
detection:
  selection:
    DestinationPort: 3389
    Initiated: "true"
  filter_main_mstsc:
    Image:
      - C:\Windows\System32\mstsc.exe
      - C:\Windows\SysWOW64\mstsc.exe
  filter_optional_dns:
    Image: C:\Windows\System32\dns.exe
    SourcePort: 53
    Protocol: udp
  filter_optional_avast:
    Image|endswith:
      - \Avast Software\Avast\AvastSvc.exe
      - \Avast\AvastSvc.exe
  filter_optional_sysinternals_rdcman:
    Image|endswith: \RDCMan.exe
  filter_optional_chrome:
    Image: C:\Program Files\Google\Chrome\Application\chrome.exe
  filter_optional_third_party:
    Image|endswith:
      - \FSAssessment.exe
      - \FSDiscovery.exe
      - \MobaRTE.exe
      - \mRemote.exe
      - \mRemoteNG.exe
      - \Passwordstate.exe
      - \RemoteDesktopManager.exe
      - \RemoteDesktopManager64.exe
      - \RemoteDesktopManagerFree.exe
      - \RSSensor.exe
      - \RTS2App.exe
      - \RTSApp.exe
      - \spiceworks-finder.exe
      - \Terminals.exe
      - \ws_TunnelService.exe
  filter_optional_thor:
    Image|endswith:
      - \thor.exe
      - \thor64.exe
  filter_optional_splunk:
    Image|startswith: C:\Program Files\SplunkUniversalForwarder\bin\
  filter_optional_sentinel_one:
    Image|endswith: \Ranger\SentinelRanger.exe
  filter_optional_firefox:
    Image: C:\Program Files\Mozilla Firefox\firefox.exe
  filter_optional_tsplus:
    Image:
      - C:\Program Files\TSplus\Java\bin\HTML5service.exe
      - C:\Program Files (x86)\TSplus\Java\bin\HTML5service.exe
  filter_optional_null:
    Image: null
  filter_optional_empty:
    Image: ""
  filter_optional_unknown:
    Image: <unknown process>
  condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
  - Third party RDP tools
level: high
license: DRL-1.1
related:
  - id: ed74fe75-7594-4b4b-ae38-e38e3fd2eb23
    type: derived