The pam_krb5 module allows Pluggable Authentication Modules aware applications to use Kerberos to verify user identities by obtaining user credentials at log in time. A flaw was found in pam_krb5. In some non-default configurations , the text of the password prompt varied based on whether or not the username provided was a username known to the system. A remote attacker could use this flaw to recognize valid usernames, which would aid a dictionary-based password guess attack. This update also fixes the following bugs: * certain applications which do not properly implement PAM conversations may fail to authenticate users whose passwords have expired and must be changed, or may succeed without forcing the user"s password to be changed. This bug is triggered by a previously-applied fix to pam_krb5 which makes it comply more closely to PAM specifications. If an application misbehaves, enabling the "chpw_prompt" option for its service should restore the old behavior. * pam_krb5 does not allow the user to change an expired password in cases where the Key Distribution Center is configured to refuse attempts to obtain forwardable password-changing credentials. This update fixes this issue. * failure to verify TGT because of wrong keytab handling. Users of pam_krb5 are advised to upgrade to these updated packages, which resolve these issues.