Which of the following allows a hidden backdoor to be used for access to workstations on the Internet?

Firmware is the low-level software embedded in hardware devices and is not inherently malicious, though it can be targeted by malware.

A rootkit is a type of malicious software that embeds itself deeply into the operating system, often at the kernel level, to conceal its presence from users and security tools. By hiding its files, processes, and network connections, a rootkit can maintain a persistent backdoor that allows attackers to access the compromised workstation over the Internet without detection. This combination of stealth and persistent unauthorized access is the defining characteristic of rootkits.

SQL injection is an attack technique targeting databases by injecting malicious SQL code through input fields, not a method for creating backdoors on workstations.

Cross-site scripting (XSS) is a web application vulnerability that injects malicious scripts into web pages viewed by other users, not a mechanism for workstation backdoor access.