What condition allows a buffer overflow to happen?

A.
Code that makes improper use of Random Access Memory

B.
Improper use of discretionary access control lists

C.
Improper checks in code with regard to the size of input data

D.
Sending large amounts of data over a network

Explanation:
Buffer overflow attacks leverage a vulnerability in code exposed when it is written without checks in place to control the amount of data allowable for input. A hacker will send the system/application more code than is needed, thus possibly allowing the excess code to be processed outside the confines of the original application. This could allow malicious code to be run.