Basic Explanation

An issue with computer programming called a buffer overflow occurs when excessive data is stored in a memory buffer. This can also be referred to as a buffer overrun. This occurs because the application failed to do a check to see how much data was being input, which resulted in the memory area being filled to capacity.

If someone is able to exploit them, buffer overflows can result in major security problems. If a hostile attacker, for instance, is able to insert code into a buffer overflow, then they may be able to access crucial user data or otherwise take control of the system.

A buffer overflow happens when a program writes more data to a memory buffer with a set length than the buffer is able to hold. This is the most basic explanation for what happens. Because of this, some of this data ends up being stored in locations other than the memory space that was allotted to it. This might result in the execution of malicious programs or other problems throughout the system.

Think of this idea as being analogous to a bathtub in order to convey it in a way that young children would have no trouble grasping the meaning of. If you fill up your bathtub but don’t turn off the water quickly enough before it overflows, then part of the water will end up on the floor of your bathroom!

This is quite similar to what takes place when a buffer overflows; there is just an excessive amount of data being written, and this leads to difficulties. It is essential for those who build computer programs to take precautions to ensure that they do not inadvertently introduce any possible vulnerabilities into the system, such as a buffer overflow.

Advanced Explanation

A buffer overflow happens when a software tries to write more data to a fixed-length memory buffer than the buffer can actually hold. This results in an error known as a buffer overflow. This causes part of the data to be written outside of the confines of the allocated buffer, which has the potential to lead to the execution of malicious code or changes in the functioning of the system. Attackers frequently take advantage of the buffer overflow vulnerability, which is one of the most widespread security flaws that can be found in computer software.

Accidental or purposeful attacks on a system can both result in buffer overflows, which can have potentially disastrous consequences. In either scenario, it is feasible for attackers to obtain access to privileged functions or resources by overwriting important parts of the system memory and gaining privileges themselves.

The fundamental ideas that underpin an attack known as a buffer overflow are straightforward:
Assign a region of memory that is greater than what is required for the storing of data; Fill up that region to its maximum capacity with data;
You need to reroute the control flow in the program such that the malicious code runs instead of the instructions that are supposed to be running.

Consider the following straightforward C program that takes user input from the command line and saves it in a character array that is 8 bytes in size:
char buffer[8]; read(0,buffer,40); /* read 40 bytes of input into 8 bytes / printf(“%s”,buffer); / print out whatever was saved in ‘buffer’ / read(0,buffer,40); / read 40 bytes of input into 8 bytes */
If more than 8 bytes are read as user input in this example, the additional bytes will overwrite whatever was previously saved in the “buffer” variable and beyond. This will occur if the user inputs more than 8 bytes. Instead of just writing out what was saved in “buffer,” as was intended by the program instructions at line 4 above, this implies that any malicious code contained inside those extra 32 bytes would run. This vulnerability may be exploited by attackers by constructing customized inputs that include malicious code and passing them to a susceptible application like the one mentioned above in the standard user input field.