There are several security bugs in Joomla 1.5 RC 1 :
1) An exploitable sql injection in the archive section . I sent the exploit
to the joomla developer, but here I am not going to publish it :)
2) A XSS bug, again in the archive section .
3) Several full path disclosure bugs . Direct access to many .../tmpl/...php
files, will expose the full installation path .
Joomla has released a new version (Joomla 1.5 RC 2) .