Cisco provides information about fixed software in Cisco bugs, which are accessible through the Cisco Bug Search Tool
When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt
and review subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to upgrade contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.