Kerberos is a network authentication system which allows clients andservers to authenticate to each other using symmetric encryption and atrusted third party, the Key Distribution Center (KDC).A use-after-free flaw was discovered in the MIT Kerberos administrationdaemon, kadmind. A remote, authenticated attacker could use this flaw tocrash the kadmind daemon. Administrative privileges are not required totrigger this flaw, as any realm user can request information about theirown principal from kadmind. (CVE-2010-0629)This update also fixes the following bug:If the service belongs to a realm other than the client's, cross-realmauthentication is required. Using a combination of client configuration andguesswork, the client determines the trust relationship sequence whichforms the trusted path between the client's realm and the service's realm.This may include one or more intermediate realms.Anticipating the KDC has better knowledge of extant trust relationships,the client then requests a ticket from the service's KDC, indicating itwill accept guidance from the service's KDC by setting a special flag inthe request. A KDC which recognizes the flag can, at its option, return aticket-granting ticket for the next realm along the trust path the clientshould be following.If the ticket-granting ticket returned by the service's KDC is for use witha realm the client has already determined was in the trusted path, theclient accepts this as an optimization and continues. If, however, theticket is for use in a realm the client is not expecting, the clientresponds incorrectly: it treats the case as an error rather than continuingalong the path suggested by the service's KDC.For this update, the krb5 1.7 modifications which allow the client to trustsuch KDCs to send them along the correct path, resulting in the clientobtaining the tickets it originally desired, were backported to krb 1.6.1(the version shipped with Red Hat Enterprise Linux 5.5). (BZ#578540)All krb5 users should upgrade to these updated packages, which containbackported patches to correct these issues. All running KDC services mustbe restarted for the update to take effect.