Buffer Overflow

Introduction - The Basics

Managing the memory of a binary:

• https://manybutfinite.com/post/anatomy-of-a-program-in-memory/

Memory Segments

• code: contains the instructions to be executed. The instructions are not linear (presence of jumps to other addresses). It is a fixed size segment, read-only. If the program is run several times, this segment will only be present once in RAM.
• data: used to store initialized global and static variables. The segment is of fixed size, readable and writable.
• bss: allows you to store uninitialized global and static variables. Fixed size segment, readable and writable.
• heap: A segment used by the programmer to allocate memory. Once used, these blocks must be deallocated. It varies in size as the program uses it. It has a growing size towards the bottom (high memory addresses).
• stack: A variable size segment that contains the environment (function activation block) of each function, its parameters, its variables, the return address.

Buffer Overflow (BOF)

The flaw: copying data without checking the size. This is a bug whereby a process, when writing to a buffer, writes outside the space allocated to the buffer, thereby overwriting information needed by the process. The aim is to make the process execute instructions.

Security

It is impossible to eradicate application vulnerabilities because the processor does not differentiate between code and data. But there are ways of protecting against them:

• ASLR (Address Space Layout Randomization): allows data zones to be placed randomly in virtual memory (position of heap, stack, libraries). This limits the effect of BOF attacks. ldd /bin/sh is used to check when a process changes address.
• Bit NX (non-executable memory page): Technique used in processors to separate areas of memory containing instructions, i.e. executable instructions, from areas containing data.