Moodle 1.5.3 is released and available from the Moodle download page as usual.
It contains fixes for all published security issues as well as many other bugs and issues that have been discovered since 1.5.2. Many thanks in particular to Petr Skoda and Catalyst for helping track and fix bugs. See the full release notes for general details, as well as security.moodle.org for more detailed information about the security-related changes.