What Is Buffer Overflow? Attacks and Risks Explained
Learn what buffer overflows are, how attackers exploit them to run arbitrary code, and how modern systems defend against these flaws.
Buffer Overflow Basics
A buffer overflow occurs when a program writes more data into a memory buffer than it was designed to hold. If input validation is missing or flawed, the extra data can overwrite adjacent memory, corrupting variables, control structures, or return addresses.
In the worst case, a carefully crafted overflow can allow an attacker to inject and execute malicious code, effectively taking control of the vulnerable program. Many classic security exploits stem from buffer overflows in network services, libraries, or system utilities.
How Attackers Exploit Buffer Overflows
To exploit a buffer overflow, attackers typically send specially crafted input designed to overwrite specific parts of memory. By overwriting a return address on the stack, for example, they can redirect execution to malicious shellcode stored elsewhere in the process memory.
Modern exploit techniques also chain multiple vulnerabilities or information leaks to bypass protections. For instance, an attacker may need to discover memory layout details before they can reliably target specific addresses, especially in systems with address space layout randomization (ASLR).
Mitigations and Secure Coding Practices
Defending against buffer overflows starts with secure coding: using safe library functions that respect buffer sizes, performing strict input validation, and favoring languages or frameworks that manage memory automatically. Code reviews and static analysis tools can help catch risky constructs before they ship.
At the platform level, defenses such as ASLR, non-executable stacks, stack canaries, and control-flow integrity make it harder to turn an overflow into a working exploit. Keeping software up to date is critical, as many security patches specifically address buffer overflow vulnerabilities discovered in the wild.