What is buffer overflow?

A buffer overflow is an irregularity that arises when software exceeds the capacity of a buffer while writing data, causing neighboring memory locations to be overwritten. To put it simply, when excessive information is inputted into a container that lacks sufficient space, this information replaces the data in adjacent containers.

Exploiting buffer overflows can be the objective of attackers who seek to manipulate a computer’s memory, ultimately compromising or gaining control over program execution.

What’s a buffer?

A data buffer, also known as a buffer, is a section of physical memory storage utilized for temporary data storage during its transfer from one location to another. These buffers are typically located in random-access memory (RAM). Buffers play a crucial role in enhancing computer performance. They are widely employed by modern hard drives to efficiently access data, and many online services rely on buffers as well. For instance, online video streaming frequently utilizes buffers to prevent interruptions. During video streaming, a portion of the video, usually around 20%, is downloaded and stored in a buffer. The video is then streamed from this buffer, ensuring that minor fluctuations in connection speed or brief service disruptions do not impact the video’s performance.

Buffers are designed with specific capacities to hold data. Unless the program utilizing the buffer includes instructions to discard excess data, the program may overwrite data in the adjacent memory space.

Buffer overflows can be exploited by attackers to corrupt software. Despite being well understood, buffer overflow attacks continue to pose significant security challenges for cybersecurity teams. In 2014, a vulnerability known as ‘heart bleeds’ exposed hundreds of millions of users to attacks due to a buffer overflow vulnerability in SSL software.

How do attackers exploit buffer overflows?

A potential threat arises when an individual intentionally provides a meticulously designed input to a program, triggering an attempt by the program to store this input in a buffer that lacks sufficient space. As a consequence, segments of memory associated with the buffer become overwritten. If the program’s memory layout is clearly defined, the attacker can selectively overwrite sections known to house executable code. Consequently, the attacker can substitute this code with their own executable code, resulting in a significant alteration of the program’s intended functionality.

For instance, if the overwritten memory segment contains a pointer (an object that directs to another location in memory), the attacker’s code could substitute it with an alternate pointer pointing to an exploit payload. This maneuver grants the attacker complete control over the entire program, allowing their code to take command.

Who is vulnerable to buffer overflow attacks?

Some programming languages are more prone to buffer overflow than others. C and C++ are widely used languages that are particularly vulnerable due to their lack of built-in safeguards against unauthorized access or modification of data in memory. These languages are utilized in the development of operating systems like Windows, Mac OSX, and Linux, which incorporate code written in one or both of them.

On the other hand, newer languages such as Java, PERL, and C# incorporate inherent functionalities designed to decrease the likelihood of buffer overflow occurrences. However, it is important to note that even though these languages have measures in place to mitigate the risk, they cannot completely eliminate the possibility of buffer overflow.

How to protect against buffer overflow attacks

Fortunately, contemporary operating systems incorporate runtime protections to effectively counter buffer overflow attacks. Let’s explore two commonly employed safeguards that significantly mitigate the risk of exploitation:

• Address space randomization: This technique randomly shuffles the memory locations of critical data areas within a process. Buffer overflow attacks typically rely on precise knowledge of the exact location of important executable code. By introducing randomness into the address spaces, it becomes extremely difficult to determine these locations accurately.

• Data execution prevention: In this approach, specific memory regions are designated as either executable or non-executable. By marking certain areas of memory as non-executable, the prevention mechanism thwarts attempts to execute code from those regions, thereby preventing exploitation.

Additionally, software developers can take proactive measures against buffer overflow vulnerabilities. They can either write code in programming languages that inherently possess built-in protections or employ specialized security procedures within their code.

Despite these precautions, it is not uncommon for new buffer overflow vulnerabilities to be discovered by developers, sometimes even after successful exploitation has occurred. In such cases, engineers must promptly address the vulnerabilities by patching the affected software and ensuring that users have access to the necessary updates.

What are the different types of buffer overflow attacks?

There exist various buffer overflow attacks employing diverse strategies and targeting different sections of code. Presented below are some of the most widely recognized ones:

• Stack overflow attack - This is the predominant form of buffer overflow attack, wherein a buffer on the call stack is deliberately flooded.
• Heap overflow attack - This attack focuses on manipulating data in the heap, which is an open memory pool.
• Integer overflow attack - An integer overflow occurs when an arithmetic operation generates an integer that exceeds the capacity of the intended storage type, leading to a buffer overflow.
• Unicode overflow - By inserting Unicode characters into an input that expects ASCII characters, a Unicode overflow provokes a buffer overflow. Unicode offers a broader range of characters compared to ASCII, accommodating languages from across the globe. Due to the larger size of many Unicode characters, they can trigger buffer overflows.

In computer systems, two memory allocation models are employed: the stack and the heap, both residing in the computer’s RAM. The stack operates on a Last-In, First-Out model, resembling the behavior of an ammunition magazine where the last inserted bullet is the first to be fired. On the other hand, the heap consists of unorganized memory and does not follow a specific order for data entry or retrieval. Since accessing memory from the stack is faster than from the heap, the heap is typically utilized for managing larger data or data that requires explicit programmer control.