Winlogon AllowMultipleTSSessions Enable

Status: test
Severity: medium
Log source: category registry_set, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects when the 'AllowMultipleTSSessions' value is enabled. Which allows for multiple Remote Desktop connection sessions to be opened at once. This is often used by attacker as a way to connect to an RDP session without disconnecting the other users

Known false positives

Legitimate use of the multi session functionality

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1112` Modify Registry
Defense Impairment	`T1112` Modify Registry

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 13: RegistryEvent (Value Set)

Rule body

title: Winlogon AllowMultipleTSSessions Enable
id: f7997770-92c3-4ec9-b112-774c4ef96f96
status: test
description: |
  Detects when the 'AllowMultipleTSSessions' value is enabled.
  Which allows for multiple Remote Desktop connection sessions to be opened at once.
  This is often used by attacker as a way to connect to an RDP session without disconnecting the other users
references:
    - http://blog.talosintelligence.com/2022/09/lazarus-three-rats.html
author: Nasreddine Bencherchali (Nextron Systems)
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

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    TargetObject|endswith: '\Microsoft\Windows NT\CurrentVersion\Winlogon\AllowMultipleTSSessions'
    Details|endswith: DWORD (0x00000001)

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Details`	ends_with	`DWORD (0x00000001)`	`field:"Details" kind:ends_with value:"DWORD (0x00000001)"`
`TargetObject`	ends_with	`\Microsoft\Windows NT\CurrentVersion\Winlogon\AllowMultipleTSSessions`	`field:"TargetObject" kind:ends_with value:"\Microsoft\Windows NT\CurrentVersion\Winlogon\AllowMultipleTSSessions"`