John Gruber writes that Apple has closed all of the known URI-related vulnerabilities with its latest Mac OS X update, Security Update 2004-06-07.
There are separate versions of the update available for Panther (10.3.4) and Jaguar (10.2.8).
Reference:
A consolidated, comprehensive, and to-the-point list of instructions for closing all known URI-related vulnerabilities affecting Mac OS X.