Multiple vulnerabilities has been found and corrected in krb5:

The kdb_ldap plugin in the Key Distribution Center (KDC) in
MIT Kerberos 5 (aka krb5) 1.9 through 1.9.1, when the LDAP
back end is used, allows remote attackers to cause a denial of
service (NULL pointer dereference and daemon crash) via a kinit
operation with incorrect string case for the realm, related to the
is_principal_in_realm, krb5_set_error_message, krb5_ldap_get_principal,
and process_as_req functions (CVE-2011-1527).

The krb5_ldap_lockout_audit function in the Key Distribution Center
(KDC) in MIT Kerberos 5 (aka krb5) 1.8 through 1.8.4 and 1.9 through
1.9.1, when the LDAP back end is used, allows remote attackers to cause
a denial of service (assertion failure and daemon exit) via unspecified
vectors, related to the locked_check_p function (CVE-2011-1528).

The lookup_lockout_policy function in the Key Distribution Center (KDC)
in MIT Kerberos 5 (aka krb5) 1.8 through 1.8.4 and 1.9 through 1.9.1,
when the db2 (aka Berkeley DB) or LDAP back end is used, allows remote
attackers to cause a denial of service (NULL pointer dereference and
daemon crash) via vectors that trigger certain process_as_req errors
(CVE-2011-1529).

The updated packages have been patched to correct these issues.