The Zend Framework vulnerability potentially allows an attacker to read any file on the web server where the Zend XMLRPC functionality is enabled. So potentially an attacker can read configuration file of your Magento installation.
It is very important to apply security patches that were released by Magento yesterday.
Magento Community Edition
You are secure if you use Magento Community 1.3.x or Magento Community 18.104.22.168.
If you use Magento Community 1.4.x, 1.5.x, 1.6.x and 1.7.x versions it is important to apply security fix from Magento as soon as possible.
Security patches are available for download:
Magento Enterprise Edition and Magento Professional Edition
You are secure if you use Magento Enterprise 22.214.171.124.
Download and apply security patch for Magento Enterprise / Professional from Download area in your Magento account.
Important: Don't forget to clear Magento cache, Magento compiler cache, APC/Memcache and any other cache mechanisms you use after patch application.