A non-admin user account on the Zabbix frontend with the default User role, or with any other role that gives API access can exploit this vulnerability. An SQLi exists in the CUser class in the addRelatedObjects function, this function is being called from the CUser.get function which is available for every user who has API access.
The product constructs all or part of an SQL command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended SQL command when it is sent to a downstream component. Without sufficient removal or quoting of SQL syntax in user-controllable inputs, the generated SQL query can cause those inputs to be interpreted as SQL instead of ordinary user data.