krb5: Reachable assertion in the KDC using S4U2Self requests

A Reachable Assertion issue was discovered in the KDC in MIT Kerberos 5 aka krb5 before 1.17. If an attacker can obtain a krbtgt ticket using an older encryption type single-DES, triple-DES, or RC4, the attacker can crash the KDC by making an S4U2Self request...