Select catalog role - Oracle
It only allows access to data dictionary views, so the only security implication is that the users(s) would be able to see which objects existed in the other schemas. They would not, however, be able to actually view the data in the other schemas.

I said there was only one security implication, but another is that they would be able to view the source of any stored procedures/functions in all schemas, by viewing DBA_SOURCE etc.