Univention Corporate Server 4.3 erratum 622 (extended maintenance)

This update addresses the following issues:
* In libvpx, there is a possible out of bounds read due to a missing bounds
  check. This could lead to remote information disclosure with no additional
  execution privileges needed. User interaction is not needed for
  exploitation (CVE-2019-9232)
* In libvpx, there is a possible out of bounds read due to a missing bounds
  check. This could lead to remote information disclosure with no additional
  execution privileges needed. User interaction is needed for exploitation
  (CVE-2019-9325)
* In libvpx, there is a possible information disclosure due to improper input
  validation. This could lead to remote information disclosure with no
  additional execution privileges needed. User interaction is needed for
  exploitation (CVE-2019-9433)