Univention Corporate Server 4.3 erratum 655 (extended maintenance)

This update addresses the following issues:
* Server NULL pointer dereference flaw in ClientCutText message handling
  (CVE-2014-6053)
* Improper input sanitization in rfbProcessClientNormalMessage in rfbserver.c
  (CVE-2018-7225)
* Infinite loop in VNC client code allows for denial of service
  (CVE-2018-20021)
* Improper initialization in VNC client code allows for information
  disclosure (CVE-2018-20022)
* TightVNC contains global buffer overflow in HandleCoRREBBP macro function,
  which can potentially result code execution. This attack appear to be
  exploitable via network connectivity. (CVE-2019-8287)
* TightVNC contains heap buffer overflow in rfbServerCutText handler, which
  can potentially result code execution.. This attack appear to be
  exploitable via network connectivity. (CVE-2019-15678)
* TightVNC contains heap buffer overflow in InitialiseRFBConnection function,
  which can potentially result code execution. This attack appear to be
  exploitable via network connectivity. (CVE-2019-15679)
* TightVNC contains null pointer dereference in HandleZlibBPP function, which
  results Denial of System (DoS). This attack appear to be exploitable via
  network connectivity. (CVE-2019-15680)
* LibVNC contains a memory leak (CWE-655) in VNC server code, which allow an
  attacker to read stack memory and can be abused for information disclosure.
  Combined with another vulnerability, it can be used to leak stack memory
  and bypass ASLR. This attack appear to be exploitable via network
  connectivity. These vulnerabilities have been fixed. (CVE-2019-15681)