In an internal security audit, the white hat hacker gains control over a user account and attempts to acquire access to another account's confidential files and information. How can he achieve this?

Privilege escalation is the technique of leveraging a compromised or low-privilege account to gain access to resources or permissions beyond the original authorization scope. Horizontal privilege escalation occurs when an attacker moves laterally to access data or functionality belonging to another user at the same privilege level - exactly what the white hat is doing here. This is accomplished by exploiting access control misconfigurations, insecure direct object references, or authentication flaws that fail to properly isolate user data.

Shoulder-surfing is a physical observation attack where an attacker watches a victim's screen or keyboard to steal credentials or sensitive information, not a technique for digital file access.

Hacking Active Directory is a specific technical attack targeting the AD directory service infrastructure itself, not the general concept of accessing another user's files from a compromised account.

Port scanning is a network reconnaissance technique used to enumerate open ports and running services on a target host, and does not provide access to another account's files.