Univention Corporate Server 4.3 erratum 661 (extended maintenance)

This update addresses the following issues:
* Out of bounds reads in sctp_load_addresses_from_init (CVE-2019-20503)
* Use-after-free when removing data about origins (CVE-2020-6805)
* BodyStream::OnInputStreamReady was missing protections against state
  confusion (CVE-2020-6806)
* Use-after-free in cubeb during stream destruction (CVE-2020-6807)
* Devtools' 'Copy as cURL' feature did not fully escape website-controlled
  data, potentially leading to command injection (CVE-2020-6811)
* The names of AirPods with personally identifiable information were exposed
  to websites with camera or microphone permission (CVE-2020-6812)
* Memory safety bugs fixed in Firefox 74 and Firefox ESR 68.6 (CVE-2020-6814)