The MITRE CVE dictionary describes this issue as:
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. NOTE: the Berkeley DB vector is covered by CVE-2011-4151.
Find out more about CVE-2011-1528 from the
MITRE CVE dictionary dictionary and
Not vulnerable. This issue did not affect the versions of krb5 as shipped with Red Hat Enterprise Linux 4 or 5.