Univention Corporate Server 4.2 erratum 456 (security)

This update addresses the following issues:
* Systems with microprocessors utilizing speculative execution and
  speculative execution of memory reads before the addresses of all prior
  memory writes are known may allow unauthorized disclosure of information to
  an attacker with local user access via a side-channel analysis, aka
  Speculative Store Bypass (SSB), Variant 4. (CVE-2018-3639)
* Systems with microprocessors utilizing speculative execution and that
  perform speculative reads of system registers may allow unauthorized
  disclosure of system parameters to an attacker with local user access via a
  side-channel analysis, aka Rogue System Register Read (RSRE), Variant 3a.
  (CVE-2018-3640)