Vulnerable TCP Server and Exploit Demonstration

7etsuo, 2024

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This repository contains a collection of files designed to demonstrate a buffer overflow exploit using Return-Oriented Programming (ROP) on a purposely vulnerable TCP server. The server is written in C, and the exploit is demonstrated using a Python script.

Warning

For Educational Use Only: This software is intended to simulate security vulnerabilities for educational purposes only. It is designed for use in a controlled, consensual environment such as security training or software testing labs. Unauthorized testing against non-consenting systems is illegal and unethical.

Components

• my_tcp.h and my_tcp.c: These files handle the basic TCP server operations, including socket initialization, binding, and client handling.
• main.c: Implements the main function of the server and includes the deliberately vulnerable function to demonstrate buffer overflow.
• gadgets.h and gadgets.c: Provide implementations of various ROP gadgets used in the exploit.
• exploit.py: A Python script that sends a payload designed to exploit the buffer overflow vulnerability in the TCP server.

Setup Instructions

Configuring Visual Studio Code

Three options to compile the server

1. Disable Security Features for Compilation: Configure your compiler to disable ASLR, stack cookies, etc., while keeping DEP enabled. This can be done in Visual Studio by setting the appropriate linker options:

   /DYNAMICBASE:NO /NXCOMPAT /GS-
   

2. Compile the Server: Open Visual Studio Command Prompt or use MinGW to compile the server:

   cl my_tcp.c main.c /Fe:vulnerable_server.exe /link /MACHINE:X86 /DYNAMICBASE:NO /NXCOMPAT /GS-

   or using MinGW:

   gcc my_tcp.c main.c -o vulnerable_server.exe -Wl,--dynamicbase=no,--nxcompat -fno-stack-protector -lws2_32

3. To compile the C server in Visual Studio Code with MinGW, set up the tasks.json file under the .vscode folder with the appropriate tasks configuration:

4. Create a .vscode directory in your project root if it doesn't already exist.

5. Create or edit the tasks.json file inside the .vscode folder to include the following task configuration:

   {
       "version": "2.0.0",
       "tasks": [
           {
               "label": "build vulnerable server",
               "type": "shell",
               "command": "gcc",
               "args": [
                   "-o",
                   "${fileDirname}\\${fileBasenameNoExtension}.exe",
                   "${fileDirname}\\${fileBasename}",
                   "-m32",  // Compiles the code to run on 32-bit Windows
                   "-Wl,-dynamicbase:no",  // Disables ASLR (Address Space Layout Randomization)
                   "-Wl,-nxcompat",        // Enables DEP (Data Execution Prevention)
                   "-fno-stack-protector"  // Disables stack protection (stack cookies)
               ],
               "group": {
                   "kind": "build",
                   "isDefault": true
               },
               "presentation": {
                   "echo": true,
                   "reveal": "always",
                   "focus": false,
                   "panel": "shared",
                   "showReuseMessage": true,
                   "clear": false
               },
               "problemMatcher": "$gcc",
               "detail": "Compiler task configured to disable ASLR, enable DEP, and disable stack protection."
           }
       ]
   }

This configuration sets up a build task that compiles the C server using GCC with flags to disable ASLR, enable DEP, and disable stack cookies, ensuring that the environment is configured for the purposes of demonstrating the vulnerability exploit.

Compile the Server

Open the command palette in VSCode (Ctrl+Shift+P), type "Run Build Task", and select the "build vulnerable server" task. This compiles the server according to the specified settings in tasks.json.

Running the Server and Exploit

• Run the Server: Navigate to the output directory in your terminal or command prompt and execute the server:

  ./vulnerable_server.exe

• Run the Exploit: Make sure the server is running and listening on the default TCP port 12345. Execute the Python script exploit.py from a command line:

  python exploit.py

Exploit Details

The Python script, exploit.py, sends a payload that exploits a buffer overflow vulnerability, manipulating the stack and using ROP to execute arbitrary code through carefully chosen gadgets.