Which of the following vulnerability types in the MOST concerning?

Given the code snippet below:

Which of the following vulnerability types in the MOST concerning?
A . Only short usernames are supported, which could result in brute forcing of credentials.
B . Buffer overflow in the username parameter could lead to a memory corruption vulnerability.
C . Hardcoded usernames with different code paths taken depend on which user is entered.
D . Format string vulnerability is present for admin users but not for standard users.

Answer: B