Heap Spraying Definition

What is Heap Spraying?

The heap is one of the memory locations where an application can write data. A heap spraying attack injects malicious code into multiple locations in the heap. By “spraying” the heap with multiple copies of the malicious code, the attacker increases the probability that the malicious code will be executed by the program.

How Does Heap Spraying Work?

Heap spraying is a technique used when exploiting buffer overflow and similar vulnerabilities. In these attacks, the attacker will develop malicious code that they plan to run on the target system. This shellcode will be written in assembly code, making it look similar to the rest of the application’s code.

Once the attacker has created their shellcode, they perform a heap spraying attack via the following steps:

• Spraying: The attacker will “spray” the heap with multiple copies of the shellcode. Since heap addresses are unpredictable, the attacker doesn’t know where the copies of the malware will be placed in the heap.
• Overflow: The attacker then exploits a buffer overflow vulnerability to change the execution flow of the program. This is accomplished by changing the target of a call or jump to point somewhere in the heap.
• Execution: The attacker has placed multiple copies of the shellcode in the heap. If they’re lucky, the redirected code execution will point to a copy of the shellcode, executing the attacker’s malicious code.

Why is Heap Spraying Used?

Often, attacks designed to achieve code execution by exploiting a buffer overflow vulnerability will target the stack. Stack-based overflows are often easier to perform than heap-based ones. However, there are also often defenses against them, such as non-executable stacks and stack canaries.

It’s also possible to achieve code execution by targeting the heap, but these attacks are more difficult to perform. Memory addresses in the heap are less predictable, so it’s harder for an attacker to drop shellcode in the stack and then redirect code execution to that point.

Heap spraying attacks are designed to increase the probability of a successful buffer overflow attack targeting the heap. The more copies of the malicious code in memory, the higher the probability of success.

Protecting Against Heap Spraying

Heap spraying is intended to bypass common defenses against stack-based overflow attacks. However, there are ways to defend against heap spraying attacks, including:

• Input Validation: Heap spraying relies on the ability to exploit buffer overflows and inject malicious code on the heap. Input validation helps to detect and block malformed or malicious user input.
• Behavioral Analysis: Execution of attacker-provided code will likely make a program behave anomalously. Behavioral analysis can detect a successful heap spraying attack.
• Patch Management: Heap spraying the exploitation of a buffer overflow vulnerability. Regular vulnerability scanning and patch applications can help to identify and fix vulnerabilities before they can be exploited by an attacker.

Conclusion

Heap spraying is a technique designed to enable an attacker to achieve code execution by exploiting buffer overflow vulnerabilities. By placing multiple copies of malicious shellcode in the heap, the attacker increases the probability that their attempts to redirect code execution will result in the program landing on and executing a copy of the attacker’s malicious code.