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

Analysis Detection

ATT&CK techniques

Lateral Movement

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
- T1021.001Remote Desktop Protocol
Collection
C2
Exfiltration
Impact

What it detects

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).

Reporting behind it

Related detections9 linkedT1021.001 — drag to rearrange

Suspicious Enabling of Remote Desktop via fDenyTSConnections Registry by DeadLock Ransomware

Suspicious Plink SSH Tunnel Execution (via process_creation)

Suspicious Remote Desktop Enabled via fDenyTSConnections Registry by Sandworm

Suspicious RDP Shadow Session Started - Native (via rdp)

Malicious RDP BlueeKeep Connection Closed - CVE-2019-0708 (via rdp)

Obfuscated RDP Tunneling Configuration Enabled for Port Forwarding (via process_creation)

Malicious RDP Shadow Session Configuration Enabled - Registry (via registry_event)

Malicious RDP Tunneling (via rdp)

Suspicious Denied RDP Login with Valid Credentials (via security)

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

Pivot detection · T1021.001 · 9 related

Changelog

v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-outbound-rdp-sessions-to-port-3389-initiated-by-non-standard-processes-ed74fe75

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

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