The Symfony project has released the latest version of their framework - Symfony 1.0.5 - largely a security fix release to help head off some issues that came up with the phpmailer utility.
I've just released symfony 1.0.5. If you use the symfony built-in phpmailer (and you do if you use the ->sendMail() method in your actions), you must upgrade to this release or apply the following patch: http://trac.symfony-project.com/trac/changeset/4380?format=diff&new=4380. PHPMailer has a remote command execution vulnerability if you have configured it to use sendmail. You can find more information about this issue here: http://larholm.com/2007/06/11/phpmailer-0day-remote-execution/
The easiest way to correct the issue is to just apply the patch to your current installation, but since there are other fixes included in the new version, you might opt for the update anyway.