Univention Corporate Server 4.1 erratum 500 (extended maintenance)

This update addresses the following issues:
* Assertion failure when using DNS64 and RPZ can lead to crash
  (CVE-2017-3135)
* An error handling synthesized records could cause an assertion failure
  when using DNS64 with "break-dnssec yes;" (CVE-2017-3136)
* A response packet can cause a resolver to terminate when processing an
  answer containing a CNAME or DNAME (CVE-2017-3137)
* named exits with a REQUIRE assertion failure if it receives a null command
  string on its control channel (CVE-2017-3138)
* An error in TSIG authentication can permit unauthorized zone transfers
  (CVE-2017-3142)
* An error in TSIG authentication can permit unauthorized dynamic updates
  (CVE-2017-3143)
* Improper fetch cleanup sequencing in the resolver can cause named to crash
  (CVE-2017-3145)
* Denial of service in DNSSEC validation via a specially crafted DNS response
  (CVE-2018-5735)