Univention Corporate Server 4.1 erratum 450 (security)

This update addresses the following issues:
* execution of arbitrary code if a file with a specially crafted modeline
  is opened (CVE-2016-1248)
* buffer overflow if a spellfile has an invalid length in it (CVE-2017-5953)
* corrupted undo file can lead to buffer overflows due to integer overflow
  in a u_read_undo memory allocation (CVE-2017-6349)
* corrupted undo file can lead to buffer overflows due to integer overflow
  in an unserialize_uep memory allocation (CVE-2017-6350)
* denial of service (invalid free) or possibly unspecified other impact via
  crafted source (aka -S) file (CVE-2017-11109)