If you don't specify an index to search against it will search the default indexes listed in your user's role's "Indexes searched by default". You can view that via the web interface by navigating to Settings>Access controls> Roles>Role name. If your user's role is restricted to only certain indexes under the "Indexes" section of the same page they will only see events from those indexes which they are permitted to. If they are permitted to the indexes you want them to search you can add index=* host=XX*
to your search or add the indexes to the "Indexes searched by default" list. (This will not search the internal indexes, for that you would need to use index=_*