Stack smashing is a type of vulnerability that can lead to serious security breaches. This vulnerability occurs when a hacker exploits a flaw in a program’s memory allocation, causing the program to crash or execute arbitrary code. In this article, we will explore what stack smashing is, how it works, and what you can do to prevent it from happening.

Stack Smashing Explained

Also known as a stack buffer overflow, stack smashing is a type of security vulnerability used by threat actors to execute malicious code on a machine. The vulnerability occurs when the stack of a computer application or operating system is forced to overflow. This problem can lead to subverting the program/OS and crashing it as a result.

A stack, which is a first-in last-out (FILO) circuit is a type of buffer that stores interim results of operations inside it. Stack smashing involves packing a stack with more data than it can hold. Skilled threat actors can intentionally overload stacks with data. The excessive data may be stored in other stacked variables, including the function return address.

When the function returns, it jumps to the malicious code on the stack, which might corrupt the entire system. As a result, the software crashed due to the adjacent data on the stack.

How Stack Smashing Works?

For threat actors to execute a stack-smashing attack, they first need to find a vulnerability in the program that allows them to overflow a buffer on the stack. This can happen when a program copies data from one buffer to another without verifying the length of the copied data or when a program reads data into a buffer without verifying the length of the read data.

The attacker can then send data to the application that overflows the buffer and replaces the return address on the stack with its own code after identifying a susceptible function. The program jumps to the attacker’s code rather than the legitimate code when the function returns, enabling the attacker to run arbitrary code on the system.

How to Protect Yourself Against Stack Smashing?

Stack Canaries

Stack canaries are used to detect a stack buffer overflow before the execution of malicious code can occur. This prevention method works by placing a small integer with a random value in memory just before the stack return pointer.

Since memory is typically overwritten in buffer overflows from lower to higher memory addresses, the canary value must also be overwritten in order to overwrite the return pointer and so take over the process.

Address Space Layout Randomization (ASLR)

ASLR (Address Space Layout Randomization) is a security technique that randomizes the memory layout of a process, making it difficult for an attacker to predict the location of specific code or data in memory.

This makes it harder for an attacker to exploit vulnerabilities in a program, as they can no longer rely on the memory layout being the same every time the program runs.

Nonexecutable Stacks

Another approach to preventing stack overflow is to enforce a memory policy on the memory region of the stack that disallows execution from the stack. To execute the shellcode from the stack, the threat actor will either have to find a way to disable the execution protection from the stack’s memory or to find a way to put their shellcode payload in an unprotected region of the memory. This prevention method has become more popular since hardware support for the no-execute flag became available in most desktop processors.

How Can Heimdal® Help You and Your Company?

Unpatched vulnerabilities still represent one of the biggest threats in cybersecurity, with reportedly 30% of businesses lacking a proper patch management policy. According to researchers, 68% of cyberattacks could have been avoided if the right patches were applied earlier. But depending on the number of machines in your company, patching can become a difficult and time-consuming operation. Fortunately, there are solutions on the market that make the patching process easier.

Heimdal®’s Patch & Asset Management is a fully automated solution that allows patches and updates to be deployed on-the-fly, from anywhere in the world, whenever you like it. The solution will allow you to patch Linux, Microsoft, and even 3rd party apps, making it highly convenient. And by being fully customizable, it can perfectly suit your company’s needs. Take it for a spin and see for yourself how beneficial automated patching can be.

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Stack smashing is a serious security vulnerability that can lead to system compromise and data theft. By understanding how stack smashing works and implementing appropriate mitigation techniques, programmers can protect their programs from these types of attacks. It is important to keep up-to-date with the latest security best practices and to always be vigilant in the face of emerging threats.

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