Univention Corporate Server 4.3 erratum 626 (extended maintenance)

This update addresses the following issues:
* Nefarious CF files can be configured to run system commands without any
  output or errors. With this, exploits can be injected in a number of
  scenarios. In addition to upgrading we recommend that users should only use
  update channels or 3rd party .cf files from trusted places.
  (CVE-2018-11805)
* A message can be crafted in a way to use excessive resources.
  (CVE-2019-12420)