Exploiting a debuggeable application

👉 Overview

👀 What ?

Exploiting a debuggable application refers to the process of using debugging tools to expose, understand, and manipulate the behavior of an application. Debuggable applications provide a wealth of information for cybersecurity professionals and malicious actors alike, including the ability to observe real-time code execution, modify program state, and even circumvent software protections.

🧐 Why ?

Understanding how to exploit a debuggable application is important for both offensive and defensive cybersecurity. For penetration testers and ethical hackers, it provides a pathway to identify vulnerabilities and assess an application's resilience to exploitation. For developers and defenders, it highlights the risks of leaving applications debuggable in production environments and underscores the need for robust security controls.

⛏️ How ?

To exploit a debuggable application, one typically needs a debugger tool like GDB or OllyDBG. The process involves attaching the debugger to the running application, setting breakpoints at strategic code locations, then inspecting and manipulating program execution as needed. It's a powerful technique but also complex, requiring a deep understanding of programming and computer architecture.

⏳ When ?

Exploiting debuggable applications has been a common practice in the world of cybersecurity and software development since the inception of debugging tools. This technique has become more prevalent with the rise of complex software systems and the continuous need for effective vulnerability assessment and penetration testing strategies.

⚙️ Technical Explanations

Debuggers work by leveraging the debugging API provided by the operating system. This API allows the debugger to halt program execution, inspect and modify the process memory, and resume execution as desired. When exploiting a debuggable application, an attacker can use these capabilities to manipulate the application's behavior. For example, they might alter a conditional jump instruction to bypass a license check, or modify an in-memory data structure to induce a buffer overflow. The possibilities are practically endless, limited only by the attacker's understanding of the application and its underlying code.

Here's a real-life example of exploiting a debuggable application using GDB, a popular debugger tool. The example involves attaching GDB to a running application and modifying the program's state to bypass a password check.

Let's consider a simple C program that asks for a password and grants access only if the correct password is entered.

#include <stdio.h>
#include <string.h>

#define PASSWORD "secret"

int main() {
    char input[16];

    printf("Enter the password: ");
    gets(input);

    if (strcmp(input, PASSWORD) == 0) {
        printf("Access granted!\\n");
    } else {
        printf("Access denied!\\n");
    }

    return 0;
}

This program takes an input from the user, compares it with the defined password ("secret"), and grants access if they match. The goal is to bypass this password check using GDB.

1. Compile the program: First, compile the program with debugging symbols using gcc.

gcc -g password.c -o password

1. Start GDB: Run GDB with the program as an argument.

gdb password

1. Breakpoint: Set a breakpoint at the line where the password check happens.

break 10

1. Run the program: Start the program execution.

run

1. Enter a dummy password: When asked for a password, enter anything. The program will pause at the breakpoint.
2. Modify the program state: At this point, you can inspect the program's memory and alter its state. Change the value of the password on the stack to "secret".

set *((char **) $rsp) = "secret"

1. Continue execution: Resume the program execution.

continue

The program now grants access, even though the entered password was incorrect. This example demonstrates how a debuggable application can be exploited using a debugger tool to modify the program's state.

🖇️ Références