Buffer Overflow Causes. ©2002, Jedidiah R. Crandall, Susan L. Gerhart, Jan G. Hogle.  http://sfsecurity.pr.erau.edu
All sorts of other far-fetched but deadly-serious things you should think about - Problem.
Sometimes seemingly reasonable assumptions are just not true.
Attackers have plenty of time and infinite creativity.
A thoroughly tested and inspected piece of software might still be vulnerable through a series of a half dozen or so clever tricks.