As a seasoned red teamer or pen tester, you are always on the lookout for new techniques and tools to achieve your objectives. One such technique that has gained popularity in recent years is heap spraying, a technique used to exploit heap vulnerabilities in software. Heap spraying is an essential skill for advanced exploit development, and this article will explore the various heap spraying techniques and how you can use them to improve your penetration testing and red teaming efforts.

Heap Spraying Basics

Heap spraying is a technique used to exploit heap vulnerabilities in software applications. Before we delve into the different heap spraying techniques, let’s explore how the heap works and why it’s vulnerable to exploitation.

In computer science, the heap is a region of memory used to store dynamic data. It’s where programs store data that they create during runtime, such as objects, arrays, and other data structures. The heap is managed by the operating system or the programming language runtime, which provides functions for allocating and deallocating memory on the heap.

Heap allocation is a process where the program requests a block of memory from the heap. The heap manager searches for a free block of memory that is large enough to satisfy the request. If a suitable block is found, the heap manager allocates the memory and returns a pointer to the beginning of the block.

Heap allocation algorithms can vary depending on the operating system and programming language runtime. One common algorithm is the “First-Fit” algorithm, which searches the heap for the first free block of memory that is large enough to satisfy the request. Another algorithm is the “Best-Fit” algorithm, which searches for the smallest free block of memory that can satisfy the request.

Heap vulnerabilities occur when a program allocates memory on the heap without properly validating the size of the allocation or the data that is written to the allocated memory. An attacker can exploit these vulnerabilities by overwriting memory buffers and executing arbitrary code.

Heap spraying is a technique that attackers use to exploit heap vulnerabilities. The goal of heap spraying is to fill the heap with a large number of objects or data structures that are created in a specific location. By doing so, attackers can take advantage of memory allocation algorithms and overflow memory buffers to execute arbitrary code.

Now that we understand the basics of heap spraying, let’s explore the different heap spraying techniques that attackers use.

Static Heap Spraying

Static heap spraying is a simple technique where the attacker floods the heap with a large number of identical objects, such as shellcode or NOP sleds. The attacker typically uses a script or program to allocate a large amount of memory and then fill it with their payload.

Static heap spraying can be effective against simple heap vulnerabilities, but it’s not very reliable against modern operating systems and runtime environments. Modern heap managers randomize the location of the heap in memory, making it difficult for attackers to locate the objects they spray.

Dynamic Heap Spraying

Dynamic heap spraying involves flooding the heap with objects that have different sizes or data values. This technique is more complex than static heap spraying and requires a deep understanding of memory allocation algorithms and heap management techniques.

The most common dynamic heap spraying technique is called “heap feng shui.” This technique involves manipulating the heap to ensure that the objects we spray are allocated in the desired location.

To perform heap feng shui, attackers use a combination of techniques to allocate objects in specific locations in the heap. These techniques can include allocating small objects to exhaust the available space in the heap, allocating medium-sized objects to fill the holes left by the small objects, and allocating large objects to create a contiguous block of memory.

Once the attackers have created the contiguous block of memory, they can spray it with their payload and exploit the vulnerable code.

Dynamic heap spraying can be very effective against modern operating systems and runtime environments that randomize the location of the heap. Attackers can use heap feng shui to manipulate the heap and locate the objects they spray in the desired location.

Blind Heap Spraying

Blind heap spraying is a technique used when the attacker doesn’t know the location of the heap in memory. This technique is more complex than static and dynamic heap spraying and requires advanced knowledge of heap internals and memory management.

One common method of blind heap spraying is to use a heap leak vulnerability to obtain the address of the heap. A heap leak vulnerability occurs when a program exposes a pointer to an object in the heap. Attackers can use this pointer to calculate the address of the heap and then use dynamic heap spraying to execute their payload.

Blind heap spraying can be very effective against modern operating systems and runtime environments that randomize the location of the heap. However, it’s a more complex technique that requires more advanced knowledge of heap internals and memory management.

Now that we understand the different heap spraying techniques, let’s explore some tools and techniques that attackers use to perform heap spraying attacks.

Tools and Techniques for Heap Spraying

JavaScript

JavaScript is a popular language used to exploit vulnerabilities in web browsers. Attackers can use JavaScript to perform heap spraying attacks against web browsers and execute arbitrary code on the victim’s machine.

One common technique is to use the “Array” object to create a large number of objects in the heap. Attackers can then use these objects to overflow memory buffers and execute their payload.

Here’s an example of how an attacker can use JavaScript to perform a heap spray attack:

var shellcode = unescape("\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90");
var heap = new Array();
for (var i = 0; i < 0x10000; i++) {
    heap[i] = shellcode;
}

In this example, we create an array called heap and fill it with the shellcode. The for loop creates 65,536 objects, each containing the same shellcode.

Heap Spray Tools

Several tools are available to automate heap spraying attacks. These tools typically use dynamic heap spraying techniques and can be customized to target specific operating systems and runtime environments.

One popular tool is “Heaplib,” which is a Python-based tool that can perform heap spraying attacks against Windows operating systems. The tool can allocate objects of different sizes and fill them with arbitrary data.

Here’s an example of how an attacker can use Heaplib to perform a heap spray attack:

git clone https://github.com/9aylas/Heaplib.git
cd Heaplib
python heaplib.py -i 192.168.1.10 -p 80 -t iexplore.exe

In this example, we use Heaplib to perform a heap spray attack against Internet Explorer on a victim machine with the IP address 192.168.1.10. The tool allocates objects of different sizes and fills them with arbitrary data.

Heap Feng Shui

Heap feng shui is a technique used in dynamic heap spraying attacks. Attackers use heap feng shui to manipulate the heap and locate the objects they spray in the desired location.

One common technique is to use the “Heap Spray Allocator” (HSA), which is a custom allocator designed for heap spraying attacks. The HSA allocates memory in specific locations in the heap, making it easier for attackers to locate the objects they spray.

Here’s an example of how an attacker can use the HSA to perform a heap spray attack:

git clone https://github.com/corelan/mona.git
cd mona
!mona hsa -p iexplore.exe -a 0x00400000 -t

In this example, we use the HSA to allocate memory in Internet Explorer at address 0x00400000. The tool allocates objects of different sizes and fills them with arbitrary data.

Real-World Examples

Heap spraying is a popular technique used by attackers to exploit vulnerabilities in software. Here are some real-world examples of heap spraying attacks:

Stuxnet Worm

The Stuxnet worm was a sophisticated cyberweapon that was designed to sabotage Iran’s nuclear program. The worm used several advanced techniques, including heap spraying, to exploit vulnerabilities in the Windows operating system.

One of the Stuxnet worm’s most significant achievements was the exploitation of a zero-day vulnerability in the Windows Print Spooler service. The worm used a heap spraying technique to exploit this vulnerability and gain remote access to the infected machine.

Aurora Attacks

The Aurora attacks were a series of cyberattacks launched against several high-profile companies in 2009 and 2010. The attackers used a combination of social engineering, spear-phishing, and heap spraying techniques to gain access to the victims’ networks.

The attackers used a heap spraying technique to exploit a vulnerability in Internet Explorer 6. The exploit used a specially crafted JavaScript to flood the heap with objects and execute arbitrary code. Once the attackers gained access to the victims’ networks, they exfiltrated sensitive data, including intellectual property and trade secrets.

Conclusion

Heap spraying is a powerful technique that attackers use to exploit vulnerabilities in software applications. As security professionals, it’s essential to understand the different heap spraying techniques and tools that attackers use and how to defend against them.

By understanding the basics of the heap, memory allocation algorithms, and heap management techniques, we can identify potential vulnerabilities and apply appropriate security controls.

We’ve explored three different heap spraying techniques: static, dynamic, and blind. We’ve also provided examples of tools and techniques that attackers use to perform heap spraying attacks, including JavaScript, heap spray tools, and heap feng shui.

It’s important to note that heap spraying attacks can be detected and prevented by implementing appropriate security controls. Some common controls include:

  1. Memory randomization: Randomizing the location of the heap in memory makes it difficult for attackers to locate the objects they spray. Modern operating systems and runtime environments implement memory randomization techniques to prevent heap spraying attacks.
  2. Heap hardening: Heap hardening techniques can prevent buffer overflows and other vulnerabilities in the heap. These techniques can include bounds checking, pointer validation, and canary values.
  3. Code signing: Code signing can prevent attackers from injecting malicious code into a program. By verifying the digital signature of the code, the operating system or runtime environment can ensure that the code is legitimate and has not been tampered with.
  4. Input validation: Input validation can prevent buffer overflows and other vulnerabilities by ensuring that input data is of the expected format and size. Programs should validate all user input and reject any data that does not conform to the expected format.

By implementing these security controls, we can prevent heap spraying attacks and other types of memory-based attacks.

In conclusion, heap spraying is a powerful technique that attackers use to exploit vulnerabilities in software applications. By understanding the different heap spraying techniques and tools that attackers use, we can identify potential vulnerabilities and apply appropriate security controls to prevent attacks. As security professionals, it’s essential to stay up to date with the latest security developments and continuously improve our skills to stay ahead of attackers.