The best answer is B. Directory traversal.
The URLs show attempts to manipulate the filename parameter in order to access sensitive files and directories on the server, especially:
/etc/
/../etc/passwd
/etc/passwd
This is a classic directory traversal attack, also known as path traversal. The attacker is trying to move outside the intended directory structure and access protected operating system files. The reference to /etc/passwd is a common indicator of an attempt to read sensitive files on Unix/Linux systems.
Why the other options are incorrect:
A). Credential replayCredential replay involves reusing captured authentication credentials, which is not what these requests show.
C). Brute-force attackA brute-force attack involves repeated guessing, usually of passwords, keys, or codes.
That is not the behavior shown here.
D). Resource exhaustionResource exhaustion involves overwhelming a system with requests or usage to reduce availability. These examples instead show attempts to access files through manipulated paths.
From a Security+ standpoint, attacks using ../ to escape directories are a well-known example of directory traversal, so B is the correct answer.