stack canary
termprogrammingsecurity
A known value placed between local buffers and the saved return address, checked before a function returns.
The name is the coal-mine metaphor: if the canary is dead, something wrote past the buffer, and the program aborts instead of returning into whatever now sits in that slot. Compilers add it automatically under flags like -fstack-protector, and it is cheap, which is why it is on by default nearly everywhere. It detects rather than prevents, and it only guards the contiguous-overwrite case, so it is one layer among several, not the answer on its own.
Also known as: stack protector, canary value