A buffer over-write is a memory corruption bug that happens when software writes more data than a buffer is designed to hold. The extra bytes spill into adjacent memory and can change variables, pointers, or control data that the program relies on. In practice, that can cause crashes, data corruption, or, in the worst case, code execution.
In cyber security, buffer over-writes matter because they often turn ordinary input handling into an attack surface. A remote attacker may trigger the flaw by sending crafted network data, a malformed file, or unusual user input to a feature that copies or processes data unsafely. Defenders look for strict bounds checking, safer programming practices, fuzzing, and memory-safe languages or runtime protections such as address space layout randomization and stack canaries. When a vendor labels a flaw a buffer over-write, it usually signals a serious memory-safety issue that should be patched quickly.