The vixie-cron package contains the Vixie version of cron. Cron is a standard UNIX daemon that runs specified programs at scheduled times.
Raphael Marichez discovered a denial of service bug in the way vixie-cron verifies crontab file integrity. A local user with the ability to create a hardlink to /etc/crontab can prevent vixie-cron from executing certain system cron jobs. (CVE-2007-1856)
All users of vixie-cron should upgrade to these updated packages, which contain a backported patch to correct this issue.