Couchbase Server exposed the '/diag/eval' endpoint which by default is available on TCP/8091 and/or TCP/18091. Authenticated users that have 'Full Admin' role assigned could send arbitrary Erlang code to the 'diag/eval' endpoint of the API and the code would subsequently be executed in the underlying operating system with privileges of the user which was used to start Couchbase. Affects Version: 4.0.0, 4.1.2, 4.5.1, 5.0.0, 4.6.5, 5.0.1, 5.1.1, 5.5.0, 5.5.1. Fix Version: 6.0.0, 5.5.2