krb5 -- Multiple vulnerabilities

MIT reports:

CVE-2017-11368:
In MIT krb5 1.7 and later, an authenticated attacker can cause an
assertion failure in krb5kdc by sending an invalid S4U2Self or
S4U2Proxy request.

CVE-2017-11462:
RFC 2744 permits a GSS-API implementation to delete an existing
security context on a second or subsequent call to gss_init_sec_context()
or gss_accept_sec_context() if the call results in an error.
This API behavior has been found to be dangerous, leading to the
possibility of memory errors in some callers. For safety, GSS-API
implementations should instead preserve existing security contexts
on error until the caller deletes them.
All versions of MIT krb5 prior to this change may delete acceptor
contexts on error. Versions 1.13.4 through 1.13.7, 1.14.1 through
1.14.5, and 1.15 through 1.15.1 may also delete initiator contexts
on error.