How Buffer Overflow Attacks Hijack Program Execution and How to Stop Them

A buffer overflow exploit occurs when user input exceeds a fixed-size stack buffer, allowing attackers to overwrite the return address and redirect CPU execution to malicious code. Exploiting this typically involves identifying a vulnerable function, calculating the exact byte offset to the return address, inserting shellcode, and using a NOP sled to improve accuracy. Modern defenses such as stack canaries, ASLR, DEP/NX, and PIE raise the difficulty of exploitation but can each be bypassed through information leaks or return-oriented programming (ROP) techniques. Heap overflows present a related threat by corrupting malloc metadata to achieve arbitrary memory writes, bypassing stack-specific protections. The root fix lies in safer coding practices — replacing unsafe functions like strcpy and gets with bounds-checking alternatives, and preferring memory-safe languages such as Rust or Go over C/C++.