Which of the following is not a common threat to access control mechanisms?

Phishing is primarily a social engineering attack that typically targets users to gain unauthorized access to sensitive information, such as login credentials. While it can lead to unauthorized access, phishing itself does not directly compromise the access control mechanisms in place. Instead, it exploits human vulnerabilities by tricking individuals into revealing their credentials.

In contrast, insider attacks, DDoS attacks, and malware are direct threats to access control systems. Insider attacks involve legitimate users exploiting their access privileges for malicious purposes. DDoS (Distributed Denial of Service) attacks aim to disrupt access to services, potentially taking down access control mechanisms and denying legitimate users entry. Malware can directly compromise systems by altering or bypassing access controls, thus posing a significant threat to security frameworks.

This distinction highlights that phishing, while a serious concern in cybersecurity, does not primarily attack the integrity or efficacy of access control mechanisms as the other options do.