What Is A Buffer Overflow Attack?
Buffers are memory storage areas that temporarily hold data while it’s transferred from one point to another. When the volume of this data exceeds the overall storage capacity, a buffer overflow or buffer overrun occurs.
These overruns can impact all types of software and usually result from failure to allocate enough buffer space or malformed inputs. If the data overwrites the code, it can force the program to behave unpredictably, generate incorrect results, lead to recurring software crashes, and cause random memory access errors. Unfortunately, attackers have uncovered different ways to identify overflows across an array of products and components.
The Reasons Behind A Buffer Overflow
An overflow may occur unintentionally, but it may also be triggered by a malicious actor sending a deliberately designed input to a system, which attempts to store the data in a buffer that isn’t large enough to handle the input. If excess data is written into the adjacent buffer, it overwrites any data kept therein.
Programming languages like C and C++ are vulnerable to these types of attacks given they don’t have a built-in defense against accessing or overwriting data stored and can easily be manipulated with common programming constructs.
The techniques used to exploit buffer overflow vulnerabilities differ depending on the operating system and programming language, but the aim is always to manipulate the memory of a machine to subvert or control the execution of programs.
How Do Attackers Exploit It?
Usually, attackers deliberately feed a carefully designed input into an existing program. This causes the program to try and store the input into a buffer space that isn’t large enough, thus overwriting other portions of memory that are connected to the program.
If the program's memory layout is well-defined, the attacker can deliberately overwrite areas known to contain executable code. The intruder will then overwrite this code with their own executable code, which will fundamentally alter the way the software is designed to operate.
A common buffer overflow example is where the overwritten part of the memory contains an object pointing to another location within the memory. The code inserted by the attacker will replace the actual code with another pointer redirecting the data to an exploit payload. By doing so, the attacker’s code will be able to take over complete control of the whole application.
Types of Buffer Overflow Attacks
There are a variety of attacks that use different techniques and target different pieces of code. Below are some of the most well-known ones:
- Stack Buffer Overflow Attack - This is the most common type of attack and involves overrunning a buffer called the stack. The stack is a part of the computer’s RAM and is a neatly organized area holding data in a last-in, first-out model
- Heap Buffer Overflow Attack - A heap is another live component of the computer’s RAM. It isn’t as organized as a stack and is generally reserved for larger data. A heap overflow attacks the data in the device’s open memory pool
- Unicode Overflow Attack - A unicode overflow can overrun a buffer by inserting unicode characters into an input that requires ASCII characters
- Integer Overflow Attack - With this type of attack, arithmetic operations result in whole numbers that are too big for the intended integer type meant for storage
Which Platforms And Environments Are Most Affected?
Almost all web and application servers, and web application environments are susceptible to buffer overflow attacks. However, the environments written in Java or Python are immune to these attacks. Programming languages like C, C++, Assembly, and Fortran are highly prone to attack. Similarly, all operating platforms are also open to overruns, but partial preventive measures can be implemented.
Ways To Prevent Buffer Overflow
In addition, developers must also stay up-to-date about the latest bug reports for their web and application servers along with other products on their internet infrastructure. They should apply patches to vulnerable programs and scan their network, websites, and servers periodically. If a developer uses custom code libraries, they must review all of the code points that accept inputs from end-users via HTTP requests and ensure appropriate size checking on all incoming inputs.
For a successful attack, the attacker needs to know the exact location of the buffer within the computer’s memory. All modern-day devices come with an built-in protection called ASLR (address space layout randomization) to tackle this threat.
Keep an eye out for bug reports and release security patches for vulnerabilities to ensure you’ll be able to avert buffer overflows.