Windows RDP Registry Settings Modified to Zero

Alerts when RDP-related registry values are set to 0, potentially weakening remote access controls.

FreeUnreviewedSigmamediumv1

windows-rdp-registry-settings-modified-to-zero-a2863fbc

title: Windows RDP Registry Settings Modified to Zero
id: 8b19a4bc-a5e2-4e25-99b0-33482484e007
related:
  - id: 3f6b7b62-61aa-45db-96bd-9c31b36b653c
    type: similar
  - id: 4b8f6d3a-9c5e-4f2a-a7d8-6b9c3e5f2a8d
    type: similar
  - id: a2863fbc-d5cb-48d5-83fb-d976d4b1743b
    type: derived
status: test
description: This rule flags registry changes to specific Remote Desktop (Terminal Services) settings where the value is set to DWORD 0x00000000. It matters because disabling restrictions or changing authentication/session controls can enable unauthorized remote access or weaken RDP defenses. The detection relies on Windows registry-set telemetry matching targeted value names ending with fDenyTSConnections, fSingleSessionPerUser, and UserAuthentication, and the data value being zero.
references:
  - https://web.archive.org/web/20200929062532/https://blog.menasec.net/2019/02/threat-hunting-rdp-hijacking-via.html
  - http://woshub.com/rds-shadow-how-to-connect-to-a-user-session-in-windows-server-2012-r2/
  - https://twitter.com/SagieSec/status/1469001618863624194?t=HRf0eA0W1YYzkTSHb-Ky1A&s=03
  - https://threathunterplaybook.com/hunts/windows/190407-RegModEnableRDPConnections/notebook.html
  - https://bazaar.abuse.ch/sample/6f3aa9362d72e806490a8abce245331030d1ab5ac77e400dd475748236a6cc81/
  - http://etutorials.org/Microsoft+Products/microsoft+windows+server+2003+terminal+services/Chapter+6+Registry/Registry+Keys+for+Terminal+Services/
  - https://admx.help/HKLM/SOFTWARE/Policies/Microsoft/Windows%20NT/Terminal%20Services
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_terminal_server_suspicious.yml
author: Samir Bousseaden, David ANDRE, Roberto Rodriguez @Cyb3rWard0g, Nasreddine Bencherchali, Huntrule Team
date: 2022-09-29
modified: 2022-11-26
tags:
  - attack.persistence
  - attack.defense-impairment
  - attack.t1112
logsource:
  category: registry_set
  product: windows
detection:
  selection:
    TargetObject|endswith:
      - \fDenyTSConnections
      - \fSingleSessionPerUser
      - \UserAuthentication
    Details: DWORD (0x00000000)
  condition: selection
falsepositives:
  - Some of the keys mentioned here could be modified by an administrator while setting group policy (it should be investigated either way)
level: medium
license: DRL-1.1

What it detects

This rule flags registry changes to specific Remote Desktop (Terminal Services) settings where the value is set to DWORD 0x00000000. It matters because disabling restrictions or changing authentication/session controls can enable unauthorized remote access or weaken RDP defenses. The detection relies on Windows registry-set telemetry matching targeted value names ending with fDenyTSConnections, fSingleSessionPerUser, and UserAuthentication, and the data value being zero.

Known false positives

Some of the keys mentioned here could be modified by an administrator while setting group policy (it should be investigated either way)

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