Cisco IOS contains a flaw that may allow a malicious user to bypass access control lists. The issue is caused by incorrect parses of extended ACLs which use the "tacacs" and "tacacs-ds" keywords. It is possible that the flaw may allow unauthorized traffic to traverse the network.
Upgrade to version indicated by Cisco product matrixx, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.