Windows privilege escalation is a critical area of concern for system administrators and cybersecurity professionals. If an attacker gains access to a low-privileged account, the ultimate goal is to escalate privileges to higher levels, often aiming for SYSTEM or Administrator privileges. In this blog, we will cover the fundamentals of Windows privilege escalation, the different types of privilege escalation, and provide detailed insights into the common techniques used by attackers. We will also explore the necessary preparation steps, and finally, discuss mitigation strategies and best practices for securing your Windows environments.
Types of Privilege Escalation
There are two primary types of privilege escalation in Windows systems:
1. Vertical Privilege Escalation (Privilege Escalation)
This occurs when an attacker gains higher-level privileges than initially assigned. For instance, a user with standard privileges may escalate to an administrator or SYSTEM account. Vertical privilege escalation is commonly targeted in attacks aiming to take full control of the system.
2. Horizontal Privilege Escalation
This refers to when an attacker gains access to another user’s privileges but does not elevate to a higher privilege level (i.e., a user with low privileges gains access to another user’s resources or data). This is often used to gather sensitive data but not necessarily to control the entire system.
In this article, we focus primarily on vertical privilege escalation, which is the most commonly exploited method by attackers seeking full control of a machine.
Preparation: Gathering System Information
Before attempting privilege escalation, attackers (or security professionals) generally perform reconnaissance to collect system information. Understanding the configuration of the system, its users, groups, and services can provide valuable insights into possible attack vectors.
1. System Information
Gathering basic system information helps to identify potential vulnerabilities that can be exploited during privilege escalation. Use the following commands to obtain relevant system information:
systeminfo— Provides information about the operating system, installed patches, build numbers, and more.wmic os get caption, version, buildnumber— Retrieves the OS version, build number, and edition of the system.
2. User and Group Information
Knowing the user and group configurations can identify targets for privilege escalation. Use these commands:
net user— Displays all user accounts on the system.net localgroup— Lists all the local groups on the system.whoami— Displays the current logged-in user.wmic useraccount list full— Provides a comprehensive list of all local user accounts.groups— Lists the groups to which the current user belongs.
3. Scheduled Tasks Information
Scheduled tasks running with elevated privileges can be leveraged for privilege escalation. Use these commands to gather information about scheduled tasks:
schtasks /query— Lists all scheduled tasks on the system.taskschd.msc— Opens the Task Scheduler GUI to inspect scheduled tasks.
By gathering this information, an attacker (or ethical hacker) can begin identifying weak configurations and potential privilege escalation opportunities.
Common Privilege Escalation Techniques
1. Exploiting Weak Configurations
Many Windows systems have misconfigured settings that provide an easy path to privilege escalation. Some of these weak configurations include:
- Weak NTFS Permissions: If files or directories are not properly secured, an attacker can alter or replace executable files to gain higher privileges. For example, if a user can write to a folder that runs executables with elevated privileges, they may exploit it.
Exploitation Example: An attacker may find a folder with weak permissions (e.g.,
EveryonehasFull Control), replace an executable with a malicious payload, and execute it with elevated privileges when the system executes the program.Mitigation: Always secure critical system files and directories. Use the principle of least privilege to assign file system permissions and regularly audit access rights.
2. Abusing Windows Services
Windows services are a common target for privilege escalation, especially if they run with higher privileges, such as the SYSTEM account. Misconfigured services may allow attackers to interact with or replace service binaries.
- Service Misconfigurations: Services running as SYSTEM or Administrator but with weak access control settings (e.g., allowing a user to modify the service binary) can be exploited to replace the executable with a malicious file.
Exploitation Example: Attackers can identify services with weak file permissions that run as SYSTEM (such as those related to SQL Server, IIS, or custom services) and replace their executables with their own malicious payload.
Mitigation: Monitor and audit services regularly. Ensure that service binaries are signed and protected, and that users only have the necessary permissions to interact with services.
3. DLL Hijacking
DLL hijacking is a technique in which an attacker places a malicious Dynamic Link Library (DLL) in a directory that is searched by a vulnerable application before the intended legitimate DLL is loaded.
- Exploitation Example: A vulnerable application may load a DLL from a user-writable directory instead of the system directory. An attacker can place a malicious DLL with the same name as the legitimate DLL and gain elevated privileges when the application loads the malicious DLL.
Mitigation: Ensure that all applications and services load DLLs from trusted directories. Implement strong security policies around file system locations where executables and DLLs are loaded.
4. Token Impersonation/Theft
Token impersonation or theft is one of the most powerful privilege escalation techniques. Windows uses security tokens to represent a user’s identity and privileges. If an attacker can steal or impersonate a valid token with higher privileges, they can escalate their privileges.
- Token Impersonation: This involves using the
Tokenclass in Windows to impersonate another user’s security token (e.g., SYSTEM or Administrator). - Token Theft: Attackers can use tools such as Mimikatz to extract tokens from memory and then impersonate a privileged user.
Exploitation Example: An attacker might extract a SYSTEM token using Mimikatz and impersonate it to execute commands with SYSTEM privileges.
Mitigation: Implement security controls like enabling Windows Defender Credential Guard, using strong authentication mechanisms, and regularly auditing and monitoring security tokens.
Mitigation and Best Practices for Preventing Privilege Escalation
1. User Account Control (UAC)
UAC is a security feature in Windows that helps prevent unauthorized changes to the system by requiring user consent for actions that require administrative privileges. Ensure UAC is enabled and configured appropriately to limit the risk of privilege escalation.
2. Patch Management
Regularly apply security patches and updates to ensure that vulnerabilities in the operating system and software are closed. Many privilege escalation techniques exploit known vulnerabilities, so keeping systems up-to-date is one of the best ways to prevent attacks.
3. Implementing Least Privilege
Adhere to the principle of least privilege (PoLP) by ensuring that users and services are only given the permissions they absolutely need. Avoid giving users administrative or SYSTEM-level access unless necessary, and restrict the use of local administrator accounts.
4. Monitoring and Auditing
Regularly monitor and audit system logs, especially for unauthorized or suspicious activity related to privilege escalation. Tools like Windows Event Logs, AuditPol, and Sysmon can provide visibility into privilege escalation attempts. Pay particular attention to changes in scheduled tasks, service modifications, and the execution of high-privilege commands.
5. Use of Security Software
Leverage security software like antivirus solutions, endpoint detection and response (EDR), and next-generation firewalls (NGFW) to detect and block malicious activities that could lead to privilege escalation.
6. Implementing Application Whitelisting
Only allow approved and signed applications to run on the system. This minimizes the chances of unauthorized executables being executed to escalate privileges.
7. Disabling Unnecessary Services
Disable any unneeded services or applications that could be vulnerable to privilege escalation attacks. Running a lean and secure system reduces the attack surface.
8. Secure Critical Files and Folders
Ensure that critical system files and folders have restrictive permissions. Regularly audit files that have elevated privileges, such as those related to system services and configurations.
Conclusion
Windows privilege escalation remains one of the most effective ways for attackers to gain complete control of a system. By understanding common privilege escalation techniques like exploiting weak configurations, abusing Windows services, DLL hijacking, and token theft, organizations can better defend themselves against such attacks. By following best practices such as implementing least privilege, maintaining regular patch management, and performing thorough system monitoring, businesses can significantly reduce the risks associated with privilege escalation and improve their overall security posture.