Buffer over-read

In computer security and programming, a buffer over-read^[1][2] or out-of-bounds read^[3] is an anomaly where a program, while reading data from a buffer, overruns the buffer's boundary and reads (or tries to read) adjacent memory. This is a special case of violation of memory safety.

Buffer over-reads can be triggered, as in the Heartbleed bug, by maliciously crafted inputs that are designed to exploit a lack of bounds checking to read parts of memory not intended to be accessible. They may also be caused by programming errors alone. Buffer over-reads can result in erratic program behavior, including memory access errors, incorrect results, a crash, or a breach of system security. Thus, they are the basis of many software vulnerabilities and can be maliciously exploited to access privileged information.^{[citation needed]}

At other times, buffer over-reads not caused by malicious input can lead to crashes if they trigger invalid page faults. For example, widespread IT outages in 2024 were caused by an out-of-bounds memory error in cybersecurity software developed by CrowdStrike.^[4]

Programming languages commonly associated with buffer over-reads include C and C++, which provide no built-in protection against using pointers to access data in any part of virtual memory, and which do not automatically check that reading data from a block of memory is safe; respective examples are attempting to read more elements than contained in an array, or failing to append a trailing terminator to a null-terminated string. Bounds checking can prevent buffer over-reads,^[5] while fuzz testing can help detect them.