Kerberos is a network authentication system which allows clients and servers to authenticate to each other using symmetric encryption and a trusted third party, the Key Distribution Center . Multiple checksum validation flaws were discovered in the MIT Kerberos implementation. A remote attacker could use these flaws to tamper with certain Kerberos protocol packets and, possibly, bypass authentication or authorization mechanisms and escalate their privileges. Red Hat would like to thank the MIT Kerberos Team for reporting these issues. This update also fixes the following bug: * When attempting to perform PKINIT pre-authentication, if the client had more than one possible candidate certificate the client could fail to select the certificate and key to use. This usually occurred if certificate selection was configured to use the value of the keyUsage extension, or if any of the candidate certificates did not contain a subjectAltName extension. Consequently, the client attempted to perform pre-authentication using a different mechanism. All krb5 users should upgrade to these updated packages, which contain backported patches to correct these issues. After installing the updated packages, the krb5kdc daemon will be restarted automatically.