What Is a Buffer Overflow Attack? Meaning, Types, and Prevention

• A buffer overflow attack is defined as a form of cybercrime where hackers intentionally pummel a data field with malicious inputs that it cannot accommodate in its assigned temporary storage (buffer). As a result, the inputs overflow into the memory space in the buffer’s proximity.
• To avoid stack overflow vulnerabilities from arising, programmers should integrate security into their development practices right from the get-go.
• This article explains the various types of buffer overflow attacks that can be perpetrated by hackers and the best practices to prevent them.

What Is a Buffer Overflow Attack?

A buffer overflow attack is a form of cybercrime where hackers intentionally pummel a data field with inputs that it cannot accommodate in its assigned temporary storage (buffer). As a result, the inputs overflow into the memory space in the buffer’s proximity. Malicious inputs can then wreak havoc, such as overwriting data, leaking sensitive information, installing malware, and even giving the hacker remote control of a system.

Simple Illustration of Buffer Overflow 

Source: BaeldungOpens a new window

Every day, hackers worldwide discover and exploit new flaws in apps, sites, and even system architecture. Memory-based programs are utilized by all electronic devices, whether old or new. This is exploited by hackers who identify weaknesses, referred to as buffer overflows.

While not entirely new, buffer overflow vulnerabilities and attacks have inflicted havoc on the digital world for a while. For instance, in November 2022, Google issued an essential update for Chrome that resolved a zero-day vulnerability. The high-severity vulnerability existed since 2022 and was exploited by attackers. Google characterized the issue as a heap buffer overflow. This was an instance of a buffer overflow attack in which heap data was overwritten to exploit a program’s functionality, which we shall discuss later in this article.

To understand what a buffer overflow attack is and how it occurs, we first need to see what a buffer is and its role.

What is a buffer?

A buffer, also known as a data buffer, is a portion of physical memory storage utilized to momentarily hold data while it is being transferred from one location to another. Typically, these reserves lie within the random access memory (RAM). Computers frequently use buffers to enhance performance. Most modern hard drives utilize buffering for efficient data access, and numerous websites also employ buffers.

For example, buffers are often employed to prevent interruptions in online video transmission. When a video is transmitted, the player receives and caches approximately 20% of the video in a buffer before streaming it. As such, modest decreases in bandwidth or brief service disruptions do not impact the performance of the video broadcast.

Attackers can exploit buffer overflows to damage software. Even though buffer overflow assaults are widely recognized, they remain a significant security issue that frustrates cybersecurity teams.

How does a buffer overflow occur?

A buffer overflow (also known as buffer overrun) occurs when the amount of data exceeds the memory buffer’s storage capacity. Consequently, the program that attempts to copy information onto the buffer overrides neighboring memory locations.

For instance, a buffer for login credentials could be constructed to accommodate a username and password input of 10 bytes. If a transaction entails an input of 14 bytes (4 bytes above what is expected), the program may write the excess data beyond the buffer boundary.

All software can be compromised by buffer overflows. This usually results from erroneous inputs or insufficient buffer space allocation. If a transaction overrides executable code, the program may operate unpredictably, producing incorrect outcomes, memory access inaccuracies, or crashes.

Certain programming languages are more vulnerable than others to buffer overflows. C++ and C are two prominent programming languages with a high level of vulnerability. This is because they lack safeguards against obtaining or modifying memory data. All versions of Windows, Mac OSX, or Linux feature code that uses either one or both of these languages.

Modern programming languages such as Java, PERL, and C# have inherent attributes that reduce the likelihood of buffer overflows; however, they cannot prevent them entirely.

See More: Java vs. JavaScript: 4 Key Comparisons

Understanding a buffer overflow attack

As explained, a buffer is a transient storage location for data. When a program or system process places more data than initially allocated for storage, the excess data overflows. This causes a portion of the data to seep into additional buffers that can corrupt or override the data they contain.

In a buffer overflow attack, a hacker engineers the extra data in a specific way with malicious intent. Typically, it contains specific directions for actions a hacker or malevolent user intends to perform. For instance, the data could initiate a response that corrupts files, modifies data, or discloses confidential information.

A buffer overflow attack is executed as follows:

• The threat actor transmits carefully crafted input to a program, known as arbitrary code.
• The program attempts to retain the data entered in a buffer that isn’t big enough.
• The surplus data is subsequently copied into the adjacent memory, overwriting existing data.
• The original data contained in the buffer contains a return pointer. It is the address where the process was meant to continue.
• However, the perpetrator can modify the parameters to direct attention to a different address.
• Typically, the attacker modifies the values to reflect the location of the exploit payload.
• This modification changes the execution path of the process and shifts control over to the attacker’s malignant code.

The meaning and severity of buffer overflow attacks can be best understood through an example. To that end, the Morris worm of 1988 is infamous for being the first online-first computer virus, which garnered significant attention from the mainstream media. It targeted a buffer overflow flaw in Unix and infected 10% of the internet in two days!

Between 1988 and 1990, over 60,00 computers were infected by the Morris worm attack. This was called the ‘Great Worm’ and the ‘Grand Daddy’ due to the damage it brought about, both in terms of system outages and the massive reputational damage it caused to internet reliability.

What causes buffer overflow attacks?

The primary cause of a buffer overflow is the failure of software developers to carry out bounds testing. Developers must pay keen attention to portions of code that utilize buffers, particularly functions that deal with user input. Take into account the subsequent lines of code:

variable $userid [10]

print “Enter Userid is:”

getstring ($userid)

This application shows ‘Enter Userid is:’ on display and accepts ‘userid’ input, with a maximum size of 10 bytes or characters. The data is then stored in the $userid variable.

The preceding code demonstrates that no bounds verification is implemented. The developer designated the variable as being 10 bytes long but did not verify the function’s limits. This renders the system vulnerable to buffer overflow attacks.

The programmer assumes the user will enter a proper name such as ‘Bill.’ However, what happens if the user inputs ‘Bill**************’? Instead of requesting genuine input, the program will most likely collapse.

As stated, programming languages such as C or C++ do not include built-in bounds verification. The initial 10 bytes are copied into the memory allotted for the $userid variable. The remaining characters will replace the following 20 bytes of RAM. This is referred to as ‘smashing the stack.’

To identify buffer overflows in the source code, you must first comprehend how the code operates. Secondly, you need to closely scrutinize the external inputs, buffer manipulations, and functions that are prone to buffer overflow, particularly gets(), strcpy(), strcat(), or printf(). If these functions are not implemented cautiously, a buffer overflow attack may be possible in the near future.

See More: What Is a Brute Force Attack? Definition, Types, Examples, and Prevention Best Practices in 2022

5 Types of Buffer Overflow Attacks

The five main types of buffer overflow attacks are as follows:

Buffer Overflow Attacks Types

1. Stack-based attack

A stack-based buffer overflow happens when a program writes more data to a stack-based buffer than the buffer can accommodate. This almost always destroys neighboring stack data and is the most prevalent form of buffer overflow exploit.

This occurs due to the finite capacity of a stack. The developer of the code has to set aside a particular quantity of capacity for the stack. If the user’s input is lengthier than the space allocated on the stack or the program does not verify that it will fit, the stack overflows. This is not a major issue on its own; however, when combined with malevolent input, it creates a significant security vulnerability.

2. Heap-based attack

A heap-based buffer overflow occurs when a significant amount of additional memory is allocated to a buffer that will be overwritten. This extra space is referred to as accumulation. Exploitation involves the destruction of stored data. The damage occurs in a manner that causes the application’s internal structures to be overwritten. This form of attack specifically targets heap data.

Programmers frequently use the heap for allocating memory, the size of which is unknown at compile time and whose size transcends the stack’s capacity. Heap-based vulnerabilities, such as the zero-day flaw uncovered in Google Chrome in 2022, tend to be more difficult to exploit than stack attacks, which is why they are less common.

3. Integer-based attack

In various programming languages, integers have a set amount of bits in memory. An integer overflow attack is caused by an arithmetic overflow error, which occurs when the outcomes of an integer function cannot be found in the allocated memory area.

Let’s say the value 192 requires 8 bits of memory to be stored. During the process, adding 64 to the initial value results in 256. This value is too large to be accommodated in the assigned memory space as it requires 9 bits. Instead of a program error, it usually ends in an unexpected outcome.

Most integer overflow scenarios can result in erroneous program behavior without introducing security flaws. In some circumstances, however, an integer excess can result in serious repercussions, such as manipulating financial calculations.

4. Unicode-based attack

Creating Unicode strings ensures that each language from every nation can be transcribed without difficulty. Arabic characters differ from English characters, for example. If one depended on the ASCII codes, it would be impossible to convert such characters. Nevertheless, this can be achieved using Unicode strings.

Unicode overflow assaults cause a buffer overflow by introducing Unicode characters inside an input set of expected ASCII characters. Numerous Unicode characters are bigger than a majority of ASCII characters, thereby creating an excess.

5. Format string-based attack

A format string exploit occurs when an application treats input data like a command or does not effectively validate input data.

If user-supplied data is perceived as a format string, it can be exploited to disclose or alter sensitive values. This allows the perpetrator to run code, extract data from the heap, or cause application segmentation faults. It could even prompt new actions jeopardizing the system’s security and stability. This is among the most dangerous types of buffer overflow attacks in the world.

See More: What Is Browser Isolation? Definition, Technology Components, and Vendors

Best Practices To Prevent Buffer Overflow Attacks

The best way to prevent a buffer overflow attack is to remove vulnerabilities at the root right when you develop the source code. To achieve this and prevent hackers from exploiting buffer vulnerabilities, follow these best practices:

Buffer Overflow Attack Prevention Best Practices

1. Always validate user inputs

When a program makes assumptions about user-supplied inputs without first validating these assumptions, buffer overflow vulnerabilities exist. Checking the extent and nature of data or copying only a particular quantity of bytes into a memory address can prevent a buffer overflow.

2. Grant applications the least privilege possible

Apps, or even users, should only be granted the permissions required to execute their duties and designated responsibilities. Implementing a least-privilege or a zero-trust strategy reduces the likelihood of a buffer overflow attack.

For instance, suppose a command prompt window shares the same rights as a corrupted application. The fewer privileges the window has, the less access an intruder has to infect the computer using the corrupted app. When feasible, only grant time-bound rights to individuals or apps and then revoke them as soon as the task is complete.

3. Use a different language when developing a new app

Most buffer overflow assaults are successful since applications neglect properly handling memory addresses or validating inputs from clients and other processes. Gets, scanf, and strcpy are examples of hazardous common library functions that aren’t bounds-checked and should be avoided in C and C++ applications. They should instead use libraries or classes designed to carry out string and various other memory operations securely.

Use a programming language that minimizes the likelihood of a buffer overflow, such as Java, Python, or C#. This best practice is possible only when designing new applications and not working on old ones, such as Google Chrome.

4. Use OS features to protect executable spaces

Executable space protection prohibits code execution on the stack or memory. Using a buffer overflow, an attacker can place arbitrary code into a program’s memory. However, via executable space protection, any attempt to execute that code will result in an exception.

Some CPUs and operating systems support the NX (No eXecute) or XD (eXecute Disabled) value. This feature allows you to designate data pages (such as the stack and the memory) as writable and readable but not actionable.

5. Incorporate fuzzing into your quality assurance roadmap

Looking for buffer overflows and fixing the flaws that cause them prevents any overflow by default. Fuzzing is an increasingly popular automated approach for discovering them.

Fuzzing or fuzz testing is an automated software testing method that entails feeding a computer program invalid, unanticipated, or arbitrary data as inputs. The program is then monitored for potential memory leakage, errors, and assertion failures. Once a possible buffer overflow has been identified, it must be rectified with a software update, security fix, or fresh release.

6. Install a compiler with a canary extension

You can also safeguard against buffer overflows by extending a compiler with canaries. Canaries are specialized values that the compiler inserts between the buffer and control data locations on the stack. Whenever a buffer overflow happens, the canary is the first object to be compromised, which means that the corruption can be detected instantaneously. Numerous compiler extensions employ canaries, such as StackGuard and ProPolice.

7. Enable protection at operating system runtime

Modern operating systems have several runtime protection measures that can prevent buffer overflow attacks against applications being executed in the OS environment. IT managers can enable these at runtime.

• Data execution prevention (DEP): It identifies memory regions as nonexecutable or executable. This prevents a buffer overflow from allowing an adversary to carry out instructions stored in a data area.
• Address space layout randomization (ASLR): This randomizes the address space coordinates of a process’s essential data areas. It consists of the stack, the heap, and the libraries. This method makes it hard for attackers to access a specific memory function reliably. They cannot cause malicious code to overflow into these most vulnerable spaces if they do not know where the executable code lies.
• Structured exception handler overwrite protection (SEHOP): Structured exception handling (SEH) is a system designed to manage hardware and software exceptions. By applying a buffer overflow attack, hackers can rewrite the SEH. SEHOP prevents malicious code from compromising the SEH.

8. Adopt pointer protection

By altering pointers, such as stored addresses, buffer overflows can occur. A pointer is a component in several programming languages that retains the memory address. During buffer overflow assaults, pointers are frequently modified to point to a remote area where the perpetrator has hosted the payload. Introducing code to such addresses safeguards these pointers by making their manipulation more difficult.

See More: What Is Botnet? Definition, Methods, Attack Examples, and Prevention Best Practices for 2022

Takeaway

Though a buffer overflow attack poses a genuine risk to any organization, there are ways to defend against them. Understanding the different kinds of attacks and how they operate will enable you to take the necessary preventative measures. In addition, keeping abreast of new attack tactics and routinely evaluating your security protocols will ensure your systems are as secure as possible. Finally, programmers should incorporate security into development practices and shift left when it comes to quality assurance to prevent stack overflow vulnerabilities in the first place.

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