Univention Corporate Server 4.3 erratum 636 (extended maintenance)

This update addresses the following issues:
* A command execution issue was found in Apache SpamAssassin: Carefully
  crafted nefarious Configuration (`.cf`) files can be configured to run
  system commands similar to CVE-2018-11805. This issue is less stealthy and
  attempts to exploit the issue will throw warnings. With this bug unpatched,
  exploits can be injected in a number of scenarios though doing so remotely
  is difficult. In addition to upgrading we again recommend that users should
  only use update channels or 3rd party `.cf` files from trusted places.
  (CVE-2020-1931)
* A command execution issue was found in Apache SpamAssassin: Carefully
  crafted nefarious rule configuration (`.cf`) files can be configured to run
  system commands similar to CVE-2018-11805. With this bug unpatched,
  exploits can be injected in a number of scenarios including the same
  privileges as `spamd` is run which may be elevated though doing so remotely
  is difficult. In addition to upgrading we again recommend that users should
  only use update channels or 3rd party `.cf` files from trusted places. If
  you cannot upgrade, do not use 3rd party rulesets, do not use `sa-compile`
  and do not run `spamd` as an account with elevated privileges.
  (CVE-2020-1930)