Thick Client Penetration Testing Checklist

Thick clients are the applications that must be installed on desktops/laptops or servers. These applications can be run on the internet or without the internet. The most common example of a thick client is the installer Skype installed on the desktop/laptop. Other examples of Thick Client are Firefox, Chrome, Microsoft Teams, Zoom, etc.

Thin clients are web applications that are running on the web browser. Generally, these web applications need an internet connection for proper functioning. The most common example is our website https://allabouttesting.org. This website needs an internet connection to fetch different blogs.

This blog provides you with a checklist to test Thick Client Applications for security. Click Here to learn more about the Architecture of Thick Client and how to carry out security testing.

Development Languages of Thick Client

• Dot Net
• Java
• C/C++
• Microsoft Silverlight

Common Tools for Thick Client Security

• CFF Explorer - Windows tool used in penetration testing to analyze and manipulate executable files. Major features like Process Viewer, PE Rebuilder, Resource Editor, Hex Editor, Import Adder, and signature management for analyzing and manipulating PE files and .NET structures.
• Echo Mirage - Pentesting tool for analyzing thick client security. It identifies vulnerabilities in client-server communication, such as insecure data transmission, authentication bypass, and API weaknesses. It aids in reverse engineering, testing encryption, and evaluating client-side security flaws.
• Sysinternals Suite - Collection of advanced Windows troubleshooting and diagnostic tools. It provides utilities for system monitoring, file management, process analysis, and security auditing. This tool helps security professionals manage systems efficiently.
• Mallory - Extensible TCP/UDP man-in-the-middle proxy designed for use as a gateway. Unlike other tools, it supports real-time modification of non-standard protocols. This feature makes it versatile for testing. It is also effective in intercepting various network communications during security assessments.
• Wireshark - Network Protocol Analyzer
• Nmap - Port Scanning Tool
• tcpdump - Command Line tool. Similar to Wireshark.
• Procmon - Sysinternals tool that provides real-time monitoring of file system, registry, and process/thread activity on Windows. It helps diagnose issues, troubleshoot system behavior, and investigate security incidents.
• OllyDbg - Popular 32-bit disassembler and debugger for Windows. It helps reverse engineers analyze executables, find vulnerabilities, and debug code, especially in malware analysis and software exploitation.
• Burpsuite - Web Application Scanner
• IDA Pro - Powerful disassembler and debugger used for reverse engineering software. It supports multiple architectures and file formats, allowing security researchers to analyze binaries, identify vulnerabilities, and understand malicious code behavior.
• Metasploit - Penetration testing framework that helps security professionals identify, exploit, and validate vulnerabilities in systems. It includes tools for exploiting known vulnerabilities, creating payloads, and automating attacks for security assessments.
• Winhex - Versatile hexadecimal editor and disk editor used for data recovery, digital forensics, and low-level file editing. It supports various formats, disk operations, and memory analysis, aiding in cybersecurity investigations.
• Testssl - Identify vulnerabilities in wireless communication
• dnspy - Popular .NET assembly editor and debugger, used for decompiling, analyzing, and editing .NET applications. It allows reverse engineers to inspect and modify assemblies, debug code, and explore .NET internals, making it useful in security research.

Common Vulnerabilities Found in Thick Client

Vulnerability	Explanation
Sensitive data leakage	Unintended exposure of passwords, API keys, etc.
Weak encryption checks	Failing to adequately verify encryption strength
Insecure Storage	Use of weak encryption techniques in storage
EXE Hijacking	Exploiting executable files for malicious purposes
DLL Hijacking	Exploiting dynamic link libraries for attacks
Improper Error Handling	Mishandling errors leading to security risks
Injection	Unsanitized input leading to code execution
Reverse Engineering	Analyzing and understanding code for exploitation
IFEO Injection	Injecting code via Image File Execution Options
Session Management	Weaknesses in managing user sessions
Buffer Overflow	Writing beyond allocated memory, causing crashes
Insecure Compilation option	Using insecure compilation settings
SSL/TLS (communication layer vulnerabilities)	Vulnerabilities in secure communication protocols
Business Logic	Exploiting flaws in application's logic
Insecure Update Management	Exploiting flaws in the application's logic

Checklist for assessment of Thick Client

1) Information Gathering

• Find the Application Architecture (two-tier or three tier) and crawl the application to gather business logic
• Platform Mapping to know architecture and infrastructure
• Find Technologies used
• Try to find the protocol used in network communication

2) Use of Tools and Techniques to identify Vulnerabilities

• Check for Authentication mechanisms
• Check for the Authorization mechanism
• Test for leaking sensitive information
• Test for Address Space Layout Randomization (ASLR)
• Test for SafeSEH
• Test for Data Execution Prevention (DEP)
• Test for strong obfuscation technique
• Try to extract the original code by using of reverse engineering method
• Verify wireless communications are secure.
• Verify High entropy
• Verify for registry-related vulnerabilities (registry manipulation, read/write access of registry keys, etc.)

3) Analyze Network Traffic

• Use a network protocol analyzer
• Try to find security issues and sensitive data while date in communication
• Try to bypass Firewall rules

4) Test for Common Vulnerabilities

• Test for OWASP TOP 10 web vulnerabilities
• Test for OWASP TOP 10 API vulnerabilities
• Try for Reverse Engineering
• Test for DLL hijacking

5) Code Review

• Use Code Scanner to scan source code for security weaknesses
• Manual Code Review to identify security flaws

Conclusion

Address these aspects systematically in your Thick Client Penetration Testing. Doing so enhances the overall security posture of the application. This approach helps mitigate potential risks. Tools like dnSpy, Metasploit, and others play vital roles in security research and penetration testing. They enable professionals to analyze, exploit, and modify software to identify vulnerabilities, strengthen defenses, and improve overall cybersecurity practices.