In versions of Couchbase Server prior to 5.0, the bucket named "default" was a special bucket that allowed read and write access without authentication. As part of 5.0, the behavior of all buckets including "default" were changed to only allow access by authenticated users with sufficient authorization. However, users were allowed unauthenticated and unauthorized access to the "default" bucket if the properties of this bucket were edited.

This has been fixed in versions 5.1.0 and 5.5.0.