How to develop exploits

You've always been curious about how hackers develop exploits to break into systems and wanted to learn the craft yourself. But where do you even start? Exploit development seems like some kind of black magic that only elite hackers who've been coding since they were five years old can perform. Good news - while it does take a lot of knowledge and practice, exploit dev is accessible to anyone willing to put in the effort to learn. Here, we'll walk through how to reverse engineer a binary, find a vulnerability, and build a working exploit from scratch. By the end, you'll have gained a new skill and will know where to start that will serve you well if you want to become an ethical hacker.

Finding a Target

The first step is finding a target to practice on. Look for open source software, programs with published source code that people actually use. Don't worry about "cracking" software, at least not yet. Instead, focus on learning the basics.

Once you've found a target, download the executable and source code. Now you need to study the program to discover any vulnerabilities. Use a disassembler like Ghidra to analyze the compiled code. Look for things like buffer overflows, integer overflows, or memory corruption bugs. These are common and can often lead to exploits.

Developing an Exploit

When you find a bug that could be exploited, figure out how to trigger it, then build a proof-of-concept exploit. Start by controlling the program's execution flow. Can you get it to execute instructions you provide? If so, you're on the right track!

From there, develop your exploit further. Try escalating your privileges, accessing sensitive data, or executing remote code. The specifics will depend on your target and the vulnerabilities you found.

Exploit development takes practice and patience. Don't get discouraged if it seems difficult at first. With time and experience, you'll be finding 0-days and writing robust exploits in no time! The key is sticking with it and not giving up. If you do that, you'll be well on your way to becoming an exploit dev pro.

Setting Up Your Reversing Environment With Ghidra or IDA Pro

If you want to get started with reverse engineering, you'll need to set up your environment. The two most popular options are Ghidra and IDA Pro. Both are disassemblers and debuggers that let you analyze compiled programs.

Ghidra is an open-source tool released by the NSA. It's free to download and runs on Windows, macOS, and Linux. Ghidra supports analyzing ARM, x86, and MIPS executables. You can view assembly code, pseudocode, and perform static analysis. Ghidra also has built-in scripting in Python and Java to automate tasks. However, Ghidra lacks a debugger, so you'll need a separate tool like Olly to debug binaries.

IDA Pro is a commercial tool used by many professionals. It has a steeper learning curve but is considered by some to be the most powerful disassembler. IDA supports a huge range of architectures and file formats. It features an embedded debugger, scripting in Python, and a massive collection of plugins and scripts. The downside is that IDA Pro is expensive.

Whether you choose Ghidra or IDA Pro, you'll have a capable reversing environment. Spend time learning the tools inside and out. Read the documentation, watch tutorial videos, and practice by analyzing some simple crackme binaries. Build up your skills by studying real-world malware and unpacking obfuscated code. With patience and persistence, you'll be well on your way to becoming a reverse engineering expert.

Identifying Vulnerabilities in Binaries

To find vulnerabilities in binaries, you'll need to analyze the executable file. This involves using a disassembler like Ghidra to reverse engineer the binary into assembly code that you can read.

Identifying Potential Vulnerabilities

Once you've reversed the binary, look for potential vulnerabilities like:

• Buffer overflows: This occurs when a program attempts to put more data in a buffer than it can hold. Hackers can exploit this by overflowing the buffer and overwriting the return address to execute malicious code.
• Format string vulnerabilities: This happens when unchecked user input is used as the format string argument in printf-like functions. Attackers can exploit this to read and write to arbitrary memory locations.
• Integer overflows: This happens when an arithmetic operation on integers generates a result that is too large to fit in the integer data type. This can often lead to buffer overflows which attackers can then exploit.
• Use-after-free: This refers to accessing memory after it has been freed, which can lead to code execution or information leaks. Look for functions like malloc() and free() to spot potential use-after-free issues.
• Logic vulnerabilities: These are vulnerabilities in the logical flow or business logic of an application. For example, improperly validating user input before using it in sensitive operations. These can often only be found through manual analysis.
• Cryptographic issues: Look for improper uses of cryptography like hardcoded keys, weak algorithms, improper IV usage, etc. These make it easy for attackers to compromise encryption and gain access to sensitive data.

The key is meticulously going through the disassembled code line by line to find anything that looks out of the ordinary or like it could be exploited. This takes patience and practice but with time you'll get better at identifying red flags and possible vulnerabilities. Keep notes on any discoveries and see if you can develop proof-of-concept exploits to confirm the issues.

Developing a Proof-of-Concept Exploit

Once you've identified a vulnerability, it's time to develop a proof-of-concept (PoC) exploit to demonstrate the impact. A PoC exploit shows how the vulnerability can be exploited, though may not provide full control. Let's walk through the basic steps to develop your PoC.

Find the Vulnerability Trigger

The first thing you need to figure out is exactly what triggers the vulnerability. This could be a buffer overflow from input that's too long, a format string vulnerability from improper string formatting, or an SQL injection from unescaped input used in a SQL query. Analyze the vulnerable code or do fuzz testing to identify the root cause.

Determine Exploitability

Not all vulnerabilities lead to exploits. Ask yourself some questions: Can I control the data that triggers the vulnerability? Can I manipulate memory or the program counter? If the answers are yes, you likely have a promising candidate for an exploit. If not, the vulnerability may still be useful as a denial-of-service attack.

Develop Your Payload

The payload is the code you want to execute when exploiting the vulnerability. It could add a user, execute a reverse shell, or drop malware. Choose a language like C, Python or Ruby and build your payload. Test it to ensure it works as intended.

Find Memory Addresses

To control program execution, you need to determine memory addresses you can jump to. Use a debugger to analyze the vulnerable program's memory and find useful instruction pointers or stack/function addresses you can redirect to.

Putting it All Together

With the components in place, you can now piece together your full PoC exploit. Deliver your payload by redirecting program control flow to it. You may need to do some trial-and-error to get the exploit to fully work. Test in a controlled environment.

A solid PoC exploit proves the vulnerability is real and demonstrates its severity. Be very careful with this sensitive information and use it only for legal and authorized purposes. Developing exploits requires a lot of practice and patience, but with time you'll be popping shells and dropping malware payloads like a pro!

Bypassing Modern Security Defenses Like ASLR and DEP

Modern security defenses like ASLR (Address Space Layout Randomization) and DEP (Data Execution Prevention) make exploit development challenging, but not impossible. There are a few common ways to bypass these protections.

ASLR randomizes the location of executable code, libraries, stacks, and heaps to make it harder for attackers to know the address of their target. ASLR can be defeated if you can leak the location of certain memory regions, like DLL mappings. A pointer leak, where a value on the stack reveals the location of a usable function pointer or ROP gadget, is one way to achieve this.

DEP prevents code from being executed from non-executable memory regions like the stack and heap. To bypass DEP, you need to find executable code that already exists in memory, like shellcode, or add new executable code through techniques like return-oriented programming (ROP) or jump-oriented programming (JOP).

• JIT Spraying

JIT (Just-In-Time) spraying is a method that sprays shellcode into memory to bypass ASLR and DEP. The shellcode is sprayed to increase the chance it will land in an executable memory region. When the shellcode is executed, it marks the memory page as executable so the full shellcode can be run.

• ROP (Return-Oriented Programming)

ROP chains together "gadgets" - small instruction sequences that end in a return - to bypass DEP and execute arbitrary code. The gadgets are strung together to emulate the functionality of normal executable code. ROP requires you to control the stack to chain the gadgets.

Bypassing modern security defenses is challenging but possible through techniques like pointer leaks, JIT spraying, and ROP. With time and patience, even the most uncrackable programs can be exploited.

With great power comes great responsibility

With great power comes great responsibility. Use your newfound talents for good - help organizations strengthen their security, not weaken it. Work to build a more ethical hacking community that values discretion and social responsibility. There will always be another binary to reverse, another exploit to develop. Stay curious and keep practicing your craft. The world needs more white hat hackers fighting the good fight.