What Is a Buffer Overflow Attack? Attack Types and Prevention Methods

Buffer overflow is one of the most common software vulnerabilities, and it usually affects C/C++ applications. Buffer overflow happens when incoming data volume exceeds what the memory buffer is designed to hold. This can happen by accident or as part of a malicious attack. Either way, buffer overflow can create opportunities for ill-intentioned hackers.

This article will discuss buffer overflow attacks in detail, describing what they are, what forms they may take, and how you can protect your enterprise from these attacks.

What is buffer overflow?

Imagine a memory buffer designed to hold log-in credentials. If the buffer expects username and password data containing 8 bits but receives 11, then you have a buffer overflow problem because the excess data will flow past the capacity of the buffer.

Memory buffers are sequential fixed-length memory segments that have been allocated for a string of characters or an array of integers. These buffers temporarily hold data while it’s being transferred between locations.

When a program or process attempts to write more data than the fixed length of the buffer can hold, the excess data has to go somewhere, so it flows into adjacent storage and overwrites or corrupts the data held there. This can result in changes to the execution flow of the program, which can cause odd program behaviors, crashes, errors, or faulty results. Buffer overflow can be used maliciously, creating an avenue for hackers to either execute arbitrary code or manipulate code to achieve their desired effect.

What is a buffer overflow attack?

If a hacker can control the input to poorly written parts of a program, they can overwrite memory segments with executable code and replace it with their own.

Attack techniques vary based on operating system and programming architecture, but the goal is always the same: to manipulate memory in order to control the way programs are executed.

Types of buffer overflow attacks

Buffer overflow attacks are usually stack based. The stack uses a last-in, first-out structure to hold data, and it has finite space. Housed within the stack is data used in function calls, including function parameters, function local variables, and management information.

A stack-based buffer overflow attack occurs when an attacker sends data containing malicious code to an application that stores its data in a stack buffer. Since the stack size is limited, the code has a specific amount of space set aside for user input. If that input is longer than the space the stack has reserved for it, it causes an overflow.

This is exactly what the attacker wants. As the attacker sends data that is too long to be held in the stack buffer, the hacker’s malicious code overwrites existing data. This includes the return pointer, which gives control of data transfers to the attacker.

How to prevent buffer overflow attacks

Fortunately, there are several ways to reduce your risk of buffer overflow attacks.

First, while buffer overflow can occur in any programming environment that allows direct memory manipulation, some programming languages are more resistant to buffer overflow than others. 

Java, JavaScript, C#, Python, and PERL have built-in safeguards against buffer overflow. Their structure reduces the likelihood of coding errors that may create overflow vulnerabilities.

Aside from programming language, it is important to ensure that operating system (OS) runtime protections are in place. Most OSs include the following runtime protections that can make successful buffer overflow attacks more difficult:

1. Address space layout randomization (ASLR) randomizes the arrangement of address space positions of key data areas. ASLR makes it harder for attackers to locate and target a particular memory function.

    

2. Structured exception handling overwrite protection (SEHOP) can thwart attacks that use the structure exception handler overwrite technique (a stack-based buffer overflow).

    

3. Data execution prevention designates memory areas as either executable or nonexecutable, preventing hackers from executing instructions written to an area of memory by overflow.
    

Preventing buffer overflow is mostly the responsibility of applications and consumers. If applications use good coding practices and consumers run on a modern OS, buffer overflow can be mitigated.