Buffer overflows are significant in cyber security due to their potential exploitation by attackers to disrupt the execution of a program and execute arbitrary code. A buffer overflow occurs when data exceeds a buffer’s storage capacity, leading to overwritten adjacent memory locations. As a result, an attacker may manipulate the application and system behaviour by inserting malicious code into the corrupted memory spaces.
Exploiting buffer overflow vulnerabilities can lead to various adverse effects, ranging from a simple crash or data corruption to a full system compromise. These vulnerabilities are commonly associated with languages that do not enforce automatic bounds checking, such as C and C++. Attackers can use buffer overflows to alter the execution flow within an application, particularly to inject malicious shellcodes or cause the program to execute functions out of sequence, potentially allowing them to gain unauthorised access to system resources.
Mitigation strategies include using safer programming languages or practices that inherently check memory bounds, implementing stack canaries, address space randomisation (ASLR), data execution prevention (DEP), and conducting thorough testing and code review to identify and correct buffer overflows before software is released.
Inadequate buffer handling practices and this type of vulnerability underscore the importance of rigorous software development practices and security auditing. Buffer overflow mitigations are essential in designing secure systems and are a focal point for developers and cybersecurity professionals.
What is a stack-based buffer overflow
The most common buffer overflow attack is stack-based buffer overflow. During this attack, the hacker sends data that contains malicious code to an application. This application then stores this data into a stack buffer, which overwrites the data already within it, including its return pointer, leading to the attacker’s control of transfers.
What is heap buffer overflow
Unlike a stack-based buffer overflow, a heap buffer overflow attack is far more challenging. This attack variation involves the hacker flooding a program’s memory space beyond its allocated memory used for current runtime operations. This type of buffer overflow can lead to data corruption, arbitrary code execution, bypass of security controls and more.
How to fix a buffer overflow
There are several potential ways to detect and fix a buffer overflow attack. For starters, scanning your computer for viruses or malware may detect any traces of a buffer overflow attack, as the specific program may have given control to a malicious user, leading to potentially malicious code or programs infiltrating your system.
Corrupted system files or Windows image files could also cause buffer overflow to be detected on your computer. To try to fix the stack-based buffer overflow, you can use System File Checker (SFC) and Deployment Image Servicing and Management (DISM).
Your system can detect a stack-based buffer overflow attack if a third-party application that starts up with the system gets corrupted. To resolve this, you can clean and boot your computer, which will prevent all third-party programs and services from starting with your system.
How to avoid buffer overflow attacks
Application developers can combat the threat of buffer overflow attacks by building security measures into their development code. They can do this by using programming languages with built-in protection or regularly testing their code to find and fix errors.
You can deploy runtime protection in current operating systems, enabling extra security against buffer overflows. One example of additional protection is Address Space Layout Randomization (ASLR). For buffer overflows to be successful, the hacker needs to know where the executable code is located. To make this harder for attackers, ASLR randomly moves the system executables to different locations of data regions.
Modern systems also have Structured Expectation Handling Overwrite Protection (SEHOP), which protects the structured exception handling system that attackers look to overwrite. During stack-based buffer overflow attacks, hackers will attempt to overwrite the exception registration record stored on the program’s stack. SEHOP prevents the malicious code the attacker uses from being able to attack the structured exception handling system by controlling its overwrite exploitation technique.
Key Characteristics:
- Involvement of writing more data than a buffer is allocated to handle
- Potential to provoke program crashes or execute arbitrary code
- Presence primarily in languages without automatic bounds checking
- Addressed via secure coding techniques and system-level protections
Examples:
- Real-World Example: The infamous Morris Worm of 1988 exploited a buffer overflow in the Unix ‘fingerd’ network service to propagate itself and cause widespread disruption on early Internet systems.
- Hypothetical Scenario: An online game’s chat function does not limit the length of messages. An attacker sends a specially crafted message that exceeds the expected length, causing a buffer overflow that overwrites critical parts of the game’s memory and allows the attacker to execute a payload granting them administrative privileges.
Related Terms:
- Memory Safety: The state in which memory access operations are checked to prevent buffer overflows and related issues.
- Shellcode: A small piece of code used as the payload in the exploitation of a software vulnerability, like a buffer overflow.
- Stack Canary: A security mechanism that can detect a stack buffer overflow before execution of malicious code can occur.
- Address Space Randomisation (ASLR): A system-level protection that helps prevent buffer overflow exploitation by randomising the location of a process’s address space.
