segfaults

Segmentation fault, commonly called segfault, is a run-time error signaling that a program has attempted to access a memory region in a way that the operating system prohibits. On many systems, the kernel sends the process SIGSEGV, terminating it and often creating a core dump for debugging.

Causes include: null or uninitialized pointer dereference; dereferencing freed or invalid memory; buffer overflows; out-of-bounds or misaligned access; use-after-free; double free; stack overflows; invalid casts or executing data as code; writing to read-only or non-writable memory. Segfaults can occur anywhere memory is accessed—on the stack, the heap, or static data—depending on the pointer used.

Detecting and diagnosing involves running under a debugger to obtain a backtrace; core dumps; tools such as Valgrind, AddressSanitizer, UBSan, and memory checkers; static analysis. In POSIX systems, SIGSEGV is the signal delivered to the process.

Prevention and mitigation include careful programming, memory-safe languages, and runtime protections. In C/C++, use smart pointers, bounds-checked containers, proper allocation/deallocation, and avoiding dangerous casts. Compile with stack canaries, enable ASLR and Data Execution Prevention, use non-executable stacks. Employ sanitizers and memory checkers during development.

Segfaults are a common class of bug in low-level software and can reflect programming errors or, if exploited with crafted input, lead to security vulnerabilities.