Improper Privilege Management
Zulip Server before 2.1.5 has Incorrect Access Control because 0198_preregistrationuser_invited_as adds the administrator role to invitations.
CWE-269 - Improper Privilege Management
An effective privilege management infrastructure provides valid users with required access and privileges across heterogeneous technology environments. An application with a faulty privilege management infrastructure allows higher than authorized privileges or enables privilege escalation. This can lead to security incidents such as system infiltration, data breach, and complete system takeover.