Windows Registry Winlogon AllowMultipleTSSessions Enabled

Alerts on enabling Winlogon AllowMultipleTSSessions (DWORD 0x00000001), allowing concurrent RDP sessions.

FreeUnreviewedSigmamediumv1

windows-registry-winlogon-allowmultipletssessions-enabled-f7997770

title: Windows Registry Winlogon AllowMultipleTSSessions Enabled
id: b2bca326-065d-44e4-8e51-9bc8d5e86913
status: test
description: This rule flags when the Winlogon registry setting AllowMultipleTSSessions is set to DWORD 0x00000001. Enabling this setting allows multiple simultaneous Remote Desktop sessions, which can help an attacker connect to an RDP session without interrupting existing user sessions. It relies on registry set telemetry that captures TargetObject and the written Details value for the specific Winlogon path.
references:
  - http://blog.talosintelligence.com/2022/09/lazarus-three-rats.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/registry/registry_set/registry_set_winlogon_allow_multiple_tssessions.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2022-09-09
modified: 2023-08-17
tags:
  - attack.persistence
  - attack.defense-impairment
  - attack.t1112
logsource:
  category: registry_set
  product: windows
detection:
  selection:
    TargetObject|endswith: \Microsoft\Windows NT\CurrentVersion\Winlogon\AllowMultipleTSSessions
    Details|endswith: DWORD (0x00000001)
  condition: selection
falsepositives:
  - Legitimate use of the multi session functionality
level: medium
license: DRL-1.1
related:
  - id: f7997770-92c3-4ec9-b112-774c4ef96f96
    type: derived

What it detects

This rule flags when the Winlogon registry setting AllowMultipleTSSessions is set to DWORD 0x00000001. Enabling this setting allows multiple simultaneous Remote Desktop sessions, which can help an attacker connect to an RDP session without interrupting existing user sessions. It relies on registry set telemetry that captures TargetObject and the written Details value for the specific Winlogon path.

Known false positives

Legitimate use of the multi session functionality

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