What Is Buffer Overflow? Preventing Buffer Overrun

Buffer overflow is one of the most common code vulnerabilities. If a buffer overflow vulnerability is not addressed, an untrustworthy agent can take advantage and cause a buffer overrun. In this blog, we break down what is buffer overflow, how to prevent buffer overflow, and we provide examples to help make safeguarding your software against buffer overflow simpler and easier.

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What Is Buffer Overflow? What Is Buffer Overrun?

Buffer overflow is a common software vulnerability. Also known as a buffer overrun, this software security issue is serious because buffer overflow exposes systems to potential cyberthreats and cyberattacks.

What Causes a Buffer Overflow / Buffer Overrun Vulnerability?

A buffer overflow or buffer overrun vulnerability happens when there is excess data in a buffer which causes the “overflow." The extra data then overruns into adjacent storage. When a buffer overflow issue occurs, it can cause a full system crash. 

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How Does a Buffer Overflow Attack Work? 

Buffer overflow is consistently one of the highest-ranking issues in the Common Weakness Enumeration (CWE) and SANS Top 25 Most Dangerous Software Errors lists. 

While buffer overflow is a well understood problem, it's still difficult to detect and prevent buffer overflow vulnerabilities in source code, as it requires consistent detection and best practices training for how best to handle these overflows. In addition, those buffer overflows that go out undetected can go on to affect thousands of vulnerable systems. 

Cyber threats can exploit a specific vulnerability in a program's memory allocation process and overflow the system by manipulating the input. By sending arbitrary or malicious code that is larger data input than the buffer can handle, attackers can change the program's execution process and gain control of the program. 

C and C++ are most vulnerable to buffer overrun attacks, as they have no built-in protection against accessing or overwriting data in their memory. More modern languages like C# and Java are less likely to be attacked, as they reduce the chance of coding errors that create buffer overflow. But wherever memory manipulation is allowed, buffer flows can happen in any environment. 

Types of Buffer Overflow Attacks

Most buffer overflow attacks can be categorized in two ways: 

Stack-based attacks. In a program's memory, the stack is a space where local variables and function calls are stored. The stack is typically empty and is set up primarily as a last-in, first-out structure, which means it is not designed to store much data at a time. Threat actors exploit stack-based buffer overflow vulnerabilities in applications by injecting files that trigger excessive memory allocation or send a concealed payload of malicious code, allowing them access to the system. 

Heap-based attacks. Unlike the stack, the heap manages dynamic memory and is managed manually. Programmers can allocate memory whose size is not known at compile time to the heap. While heap-based vulnerabilities are harder to exploit, heap-based overflow attacks can have a larger impact on the system and are therefore a draw for theat actors. Heap-based attacks flood the memory space reserved for the program beyond memory used for current runtime operations. 

There are many examples of buffer overrun / buffer overflow, including: 

• ABV.ANY_SIZE_ARRAY
• ABV.GENERAL
• ABV.ITERATOR
• ABV.MEMBER
• ABV.STACK
• ABV.TAINTED
• ABV.UNICODE.BOUND_MAP
• ABV.UNICODE.FAILED_MAP
• ABV.UNICODE.NNTS_MAP
• ABV.UNICODE.SELF_MAP
• ABV.UNKNOWN_SIZE
• NNTS.MIGHT
• NNTS.MUST
• NNTS.TAINTED
• RABV.CHECK
• RN.INDEX
• SV.FMT_STR.BAD_SCAN_FORMAT
• SV.STRBO.BOUND_COPY.OVERFLOW
• SV.STRBO.BOUND_COPY.UNTERM
• SV.STRBO.BOUND_SPRINTF
• SV.STRBO.UNBOUND_COPY
• SV.STRBO.UNBOUND_SPRINTF
• SV.UNBOUND_STRING_INPUT.CIN
• SV.UNBOUND_STRING_INPUT.FUNC

Detecting Buffer Overflow in C Vulnerability and Preventing Buffer Overflow / Buffer Overrun Attacks

In addition to secure coding best practices, best way to detect this type of vulnerability is to use a static code analyzer, such as Klocwork.

Klocwork has an extensive set of software security checkers to help ensure that security vulnerabilities cannot be exploited. Each checker provides a description of the violation, an explanation of the potential vulnerabilities and risks, and an example of the code.

Preventing Buffer Overflow in C and Other Languages

Here's how to prevent this software security vulnerability.

Use a Coding Language That Doesn't Allow For Software Vulnerabilities

One way to completely prevent cyberattacks is to use a coding language that doesn’t allow for them. For example, C is a primary target for buffer attacks because the language enables the vulnerability through direct access to memory.  On the other hand, languages like Java, Python, and .NET, are immune to buffer vulnerabilities. 

Be Aware of Buffer Usage During Development

Another way to prevent software vulnerabilities is to be aware of buffer usage during development. Where buffers are accessed is where the vulnerabilities will occur, especially if the functions deal with user-generated input.  

Follow Best Practices to Prevent Buffer Overflow

In addition, here are five best practices: 

1. Leveraging automated code review and testing.
2. DevOps training on the concepts of using unsafe functions. 
3. A focus on safe functions like strncpy vs strcpy and strncat vs strcat.
4. Keeping application servers patched. 
5. Using code analysis tools to periodically check applications for software security flaws.

Prevent a Buffer Overflow Vulnerability with Klocwork

To absolutely ensure your application is safe from damaging software vulnerabilities attacks like buffer overflow, the best course of action is to use static code analysis. As mentioned, C and C++ are particularly vulnerable to overflow. To protect C and C++ applications, you can use an SCA tool like Klocwork or Helix QAC and run a coding standard like MISRA or CERT to identify software vulnerabilities.  

SAST  tools are important for detecting security vulnerabilities across software applications.  With SCA tools, security vulnerability issues can be found as code is being developed.  

If your organization wants proactive protection against security threats, a static code analysis tool like Klocwork can help. Register for a free trial to see how Klocwork helps you to prevent vulnerabilities.

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