How does heap spray work

Improve this question. Piotr Czapla Piotr Czapla See darkreading. Add a comment. Active Oldest Votes.

If I understand correctly, They commonly take advantage from the fact that these heap blocks will roughly be in the same location every time the heap spray is run.

They're talking about a situation like this: char buffer[10]; FuncPtr p; And when you read into buffer there's no overflow protection, and you can write directly into the memory location for p. Improve this answer.

Blindy Blindy It seams I've missed that sentence on the wikipedia : Thanks! Sign up or log in Sign up using Google. This article will be helpful for developers who build antivirus and anti-exploit solutions, develop low-level user mode solutions for Windows, or want to know how to mitigate heap spraying attacks. Heap spraying is a technique used in exploits to facilitate execution of the arbitrary code. The idea is to deliver a shellcode at a predictable address in the targeted application in order to execute this shellcode using a vulnerability.

When implementing dynamic memory managers, developers face lots of challenges, including heap fragmentation. A common solution is to allocate memory in chunks of a fixed size. Heap spraying makes a targeted process continuously allocate memory with required content block by block, banking on one of the allocations placing shellcode at the required address without checking any conditions.

As you can see, a heap spray exploit technique looks like continuous spam in the form of chunks of the same size with the same content. If a heap spraying attack succeeds, control is passed to one of these chunks. To execute this attack, malicious actors need an opportunity to allocate lots of memory of the required size in the target process and to fill those allocations with identical content.

This requirement may seem too bold, but the most common cases of heap spraying attacks include compromising web app vulnerabilities. Any application that supports scripting languages for example, Microsoft Office with its Visual Basic is a potential victim for a heap spraying attack.

Thus, it makes sense to expect an attack in the context of one flow, since scripts are usually executed in a single flow. However, attackers can execute a heap spraying attack not only using scripting languages. Other methods include loading image files into the process and spraying the heap with a very high allocation granularity through the use of technologies introduced with HTML5. The heap is also randomized and if you want to change that you need to set this flag:. Try recompiling and running the program a few times to check to see if the address of your malloc calls are not randomized.

Lets ignore the gcc flags since those are related to the buffer overflow exploit. We spray our malicious code all over the heap. Because we have that command, we can add millions of NOP codes onto the front of our malicious shellcode.

By adding tons of NOPs onto the heap, we decrease the entropy of the randomized heap address space. In more complex programs eg.

For that reason, browsers have to work really hard to ensure that memory allocations have unpredictable locations. The basic idea is similar to spray painting a wall to make it all the same color. Like a wall, the heap is "sprayed" so that its "color" the bytes it contains is uniformly distributed over its entire memory "surface. The heap is vulnerable to this kind of attack because it usually starts at a predetermined location in memory.

The goal of the attack is to ensure that the bytes can be accessed later as the vector of a separate attack.