In MIT Kerberos 5 (aka krb5) 1.7 and later, an authenticated attacker can cause a KDC assertion failure by sending invalid S4U2Self or S4U2Proxy requests.
www.securityfocus.com/bid/100291
access.redhat.com/errata/RHSA-2018:0666
github.com/krb5/krb5/commit/ffb35baac6981f9e8914f8f3bffd37f284b85970
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