Joomla! 3.3.6 realese relates to the Joomla 3.3.5 released the day before. The latest version includes two security issues resolved concerning 3.3.5 version.

9 bugs in the latest Joomla! version have been fixed including problems like:

• Password reset don't work in Joomla 3.3.5
• Error when adding tags via keyboard

Security issues fixed:

• High Priority - Inadequate checking allowed the potential for remote files to be executed.
• Medium Priority - Inadequate checking allowed the potential for a denial of service attack.

Check more info here.