STACK-BASED BUFFER OVERFLOW

In a stack-based buffer overflow, controlling the EIP (Extended Instruction Pointer) is critical, as it determines the next instruction the CPU executes. Overflowing a buffer on the stack can overwrite adjacent memory, including the saved EIP, which normally holds the return address of the current function. By carefully crafting a payload that replaces the EIP with the address of malicious shellcode or a jump instruction that redirects execution to the shellcode, an attacker can hijack the program's flow and execute arbitrary code. Controlling the EIP is essential for redirecting execution, making it the cornerstone of exploiting stack-based buffer overflows. Modern systems mitigate these attacks using protections such as stack canaries, non-executable stacks (NX), and address space layout randomization (ASLR).

MITIGATIONS

Buffer overflows can be effectively mitigated through security-conscious programming, where developers carefully design software to avoid common vulnerabilities. In addition to careful coding practices, several security mechanisms help protect programs from exploitation. Canaries are special values placed on the stack that detect overwrites during a buffer overflow, allowing the operating system to terminate compromised programs. Address Space Layout Randomization (ASLR) randomizes memory locations, making it difficult for attackers to predict addresses for successful exploitation. Data Execution Prevention (DEP) enforces that certain memory areas cannot be executed as code, preventing injected or unauthorized code from running. Together, these mechanisms help developers and the OS prevent buffer overflow attacks by detecting memory corruption (canaries), making memory layout unpredictable (ASLR), and enforcing executable memory rules (DEP).

• ASLR: will randomize addresses (so you can’t reliably jump to absolute addresses across runs). For local lab testing you often temporarily disable ASLR (e.g., setarch \uname -m` -R ./vulnerable`) but never on production.

• NX/DEP: prevents execution of injected shellcode on the stack. That forces use of ROP or return-to-libc style attacks.

• Stack canaries: will detect and abort certain overwrites before return, so you must leak the canary or bypass protections.

• PIE: position independent executables randomize code region addresses, requiring info leaks or relative gadgets.