Skip to main content

Home Segmentation fault

Segmentation fault

(also segfault)

Segmentation fault definition

A segmentation fault is a computing error that occurs when a program tries to access a memory location it is not allowed to — for example, by attempting to access memory that has been deallocated. A segmentation fault is a critical error and may result in the program being terminated.

See also: memory allocation, buffer overflow attack

Common segmentation fault causes

  • One common cause of segmentation faults is attempting to dereference a null pointer (trying to access the memory pointed to by a pointer that is currently set to “null” or “nullptr,” which is simply not accessible).
  • Accessing memory regions that are outside the bounds of an allocated data structure (for example, trying to access an element past the end of an array) is another common cause of segmentation faults.
  • When a program writes data beyond the bounds of an allocated memory buffer, it can overwrite adjacent memory areas that do not belong to it. This is a classic security vulnerability known as a “buffer overflow.”
  • A segmentation fault can occur if a program's call stack grows too large due to excessive function calls (also known as a “stack overflow”). Each function call consumes stack memory, and if it exhausts the available space, it can't operate correctly.
  • Once memory is deallocated, any attempt to access it can lead to a segmentation fault. This is often referred to as a “use-after-free” error.