chef-server-api/app/controllers/users.rb in the API in Chef before 0.9.0 does not require administrative privileges for the create, destroy, and update methods, which allows remote authenticated users to manage user accounts via requests to the /users URI.

chef-server-api/app/controllers/cookbooks.rb in Chef Server in Chef before 0.9.18, and 0.10.x before 0.10.2, does not require administrative privileges for the update and destroy methods, which allows remote authenticated users to (1) upload cookbooks via a knife cookbook upload command or (2) delete cookbooks via a knife cookbook delete command.

chef-server-api/app/controllers/clients.rb in Chef Server in Chef before 0.9.20, and 0.10.x before 0.10.6, does not require administrative privileges for creating admin clients, which allows remote authenticated users to bypass intended access restrictions by leveraging read permission for the validation key and executing a knife client create command with the --admin option.