The calculated severity for Plugins has been updated to use CVSS v3 by default. Plugins that do not have a CVSS v3 score will fall back to CVSS v2 for calculating severity. Severity display preferences can be toggled in the settings dropdown.
The remote host is missing a security update.
The remote CentOS system is missing a security update which has been documented in Red Hat advisory RHSA-2011-0303.
Update the affected package(s) using, for example, 'yum update'.