t1505-005-terminal-services-dll

name	T1505.005_terminal-services-dll
description	Adversaries may abuse components of Terminal Services to enable persistent access to systems.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1505.005","persistence","windows","sub-technique"]
technique_id	T1505.005
tactic	persistence
all_tactics	["persistence"]
platforms	["Windows"]
mitre_url	https://attack.mitre.org/techniques/T1505/005
tech_stack	["windows"]
cwe_ids	["CWE-276"]
chains_with	["T1505","T1505.001","T1505.002","T1505.003","T1505.004","T1505.006"]
prerequisites	["T1505"]
severity_boost	{"T1505":"Chain with T1505 for deeper attack path","T1505.001":"Chain with T1505.001 for deeper attack path","T1505.002":"Chain with T1505.002 for deeper attack path"}

T1505.005 Terminal Services DLL

Sub-technique of: T1505

High-Level Description

Adversaries may abuse components of Terminal Services to enable persistent access to systems. Microsoft Terminal Services, renamed to Remote Desktop Services in some Windows Server OSs as of 2022, enable remote terminal connections to hosts. Terminal Services allows servers to transmit a full, interactive, graphical user interface to clients via RDP.

Windows Services that are run as a "generic" process (ex: svchost.exe) load the service's DLL file, the location of which is stored in a Registry entry named ServiceDll. The termsrv.dll file, typically stored in %SystemRoot%\System32\, is the default ServiceDll value for Terminal Services in HKLM\System\CurrentControlSet\services\TermService\Parameters\.

Adversaries may modify and/or replace the Terminal Services DLL to enable persistent access to victimized hosts. Modifications to this DLL could be done to execute arbitrary payloads (while also potentially preserving normal termsrv.dll functionality) as well as to simply enable abusable features of Terminal Services. For example, an adversary may enable features such as concurrent Remote Desktop Protocol sessions by either patching the termsrv.dll file or modifying the ServiceDll value to point to a DLL that provides increased RDP functionality. On a non-server Windows OS this increased functionality may also enable an adversary to avoid Terminal Services prompts that warn/log out users of a system when a new RDP session is created.

Kill Chain Phase

• Persistence (TA0003)

Platforms: Windows

What to Check

• Identify if Terminal Services DLL technique is applicable to target environment
• Check Windows systems for indicators of Terminal Services DLL
• Verify mitigations are bypassed or absent (2 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Simulate Patching termsrv.dll

Simulates patching of termsrv.dll by making a benign change to the file and replacing it with the original afterwards. Before we can make the modifications we need to take ownership of the file and grant ourselves the necessary permissions.