What kind of disaster? Wouldn't OS security prevent userspace program do destructive things?
It depends.
You can corrupt memory in such a way that allows executing arbitrary code, in which you could do anything that the process has privilege to do, which is probably reading and writing files as the current user and a lot more.
A userspace process can be capable of pretty destructive things, and they're all on the menu in C, especially without Valgrind.
It depends.
You can corrupt memory in such a way that allows executing arbitrary code, in which you could do anything that the process has privilege to do, which is probably reading and writing files as the current user and a lot more.