Kerberos 5 su (k5su) in FreeBSD 4.4 and earlier relies on the getlogin system call to determine if the user running k5su is root, which could allow a root-initiated process to regain its privileges after it has dropped them.
KTH Kerberos IV allows local users to change the configuration of a Kerberos server running at an elevated privilege by specifying an alternate directory using with the KRBCONFDIR environmental variable, which allows the user to gain additional privileges.
KTH Kerberos IV allows local users to specify an alternate proxy using the krb4_proxy variable, which allows the user to generate false proxy responses and possibly gain privileges.