What a buffer overflow is
A buffer overflow is a software flaw that occurs when a program writes more data into a block of memory, called a buffer, than that block was designed to hold. The extra data spills over into adjacent memory, overwriting whatever was there. At best this corrupts data and crashes the program; at worst it lets an attacker take control of the program entirely. It is one of the oldest and most serious classes of security bugs.
Why it happens
Buffers are fixed-size regions set aside to hold data such as text a user types. If a program copies input into a buffer without checking that the input fits, a long enough input runs off the end. Programming languages like C and C++ are especially prone to this because they let developers manage memory directly and do not automatically check these boundaries, so a missing check can quietly open a hole.
How attackers exploit it
Attackers craft input specifically sized to overflow a buffer and overwrite important nearby values. A classic target is the return address on the stack, which tells the program where to continue after a function finishes. By overwriting it, an attacker can redirect execution to code of their choosing, sometimes code they smuggled in as part of the oversized input, turning a simple bug into full remote control of the system.
The damage it can cause
Buffer overflows have been behind some of history's most damaging security incidents, including fast-spreading internet worms that exploited the same flaw across thousands of machines. Because a successful overflow can let an attacker run arbitrary code, it can lead to stolen data, installed malware, or a complete takeover of the affected computer. This is why the bug class has received so much attention from both attackers and defenders.
How it is prevented
Defenses exist at several levels. Careful programming checks the length of input before copying it, a practice called bounds checking, and safer library functions enforce limits. Operating systems add protections such as address space layout randomization, which shuffles where things sit in memory, and marking memory regions as non-executable. Modern languages like Rust, Java, and Python manage memory safely by design, preventing most overflows outright.
The bottom line
A buffer overflow happens when a program writes past the end of a memory buffer, corrupting nearby data and potentially letting an attacker run their own code. It stems largely from missing bounds checks in low-level languages, and it is countered by careful coding, operating-system protections, and memory-safe languages. It remains a cornerstone topic in security because its consequences can be so severe.
Related on Skillo
See also: What is a zero-day vulnerability? Explained, What is a computer worm? Explained.
Sources
Published date reflects the original event date (2026-10-23). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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