The Joomla Project announces the immediate availability of Joomla 1.5.11 [Vea]. This is a security release and users are strongly encouraged to upgrade immediately.
This release contains 26 bug fixes, two moderate-level security fixes and one low-level security fix. It has been 11 weeks since Joomla 1.5.10 was released on March 28, 2009. The Development Working Group's goal is to continue to provide regular, frequent updates to the Joomla community.
You should read this before installing: http://docs.joomla.org/Category:Version_1.5.11_FAQ
The release of 1.5.11 has just been released having taken a little longer at the end than originally planned. The main reason for it was a very large patch for issue # 15736.
This issue in on the borderline between a low-level security fix and a "best-practices" fix. The developers discovered that there were a lot of places in the layouts where they were not "escaping" certain values during output.
Version 1.5.11 contains several other low-level security fixes as well as a number of useful bug fixes. Since version 1.5 is now very stable, these fixes are generally more subtle than perhaps some of the fixes in earlier releases. Nevertheless, I encourage you to upgrade to the best Joomla! version yet.
Read more about the path towards Joomla 1.5.11: Version 1.5.11 (Finally)