Mahara 15.04 before 15.04.8 and 15.10 before 15.10.4 and 16.04 before 16.04.2 are vulnerable to some authentication methods, which do not use Mahara's built-in login form, still allowing users to log in even if their institution was expired or suspended.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.