performing-thick-client-application-penetration-test

Thick client penetration testing follows four phases: static analysis (decompile with dnSpy or Ghidra), dynamic analysis (monitor with Procmon and Wireshark), vulnerability testing (DLL hijacking, memory analysis, auth bypass), and API security testing with Burp Suite. Each finding should be proven with artifacts like decompiled code or memory dumps.

Common tools include dnSpy for .NET decompilation, JD-GUI for Java, Ghidra or IDA Pro for native binaries, Procmon for file and registry monitoring, Burp Suite for HTTP interception, Echo Mirage for raw TCP/UDP traffic, and Frida for bypassing certificate pinning.

Certificate pinning can be bypassed by patching the certificate validation logic directly in dnSpy for .NET applications, or by using Frida to hook SSL validation functions at runtime. For non-HTTP protocols, Echo Mirage can inject into the process to intercept raw TCP/UDP traffic.

Use Procmon filtered on the application process with Result = NAME NOT FOUND and paths ending in .dll to find libraries loaded from writable directories. Placing a crafted DLL in that location achieves code execution when the application loads it before the legitimate version.

The most missed issues are cleartext secrets in local storage (config files, registry, SQLite databases), hardcoded credentials only visible after decompilation, DLL hijacking via writable paths, and backend APIs that trust the client without server-side authorization checks like IDOR or mass assignment.

Thick client testing is legal only with written authorization from the system owner, such as during a contracted security assessment. Testing applications or systems you do not own or lack permission to test may violate computer fraud laws.