Univention Corporate Server 4.3 erratum 319 (security)

This update addresses the following issues:
* heap-based buffer overflow in mspack/lzxd.c (CVE-2017-6419)
* Stack-based buffer over-read in cabd_read_string function (CVE-2017-11423)
* off-by-one error in the CHM PMGI/PMGL chunk number validity checks
  (CVE-2018-14679)
* off-by-one error in the CHM chunk number validity checks (CVE-2018-14680)
* Out-of-bounds Write in kwajd_read_headers in mspack/kwajd.c
  (CVE-2018-14681)
* off-by-one error in the TOLOWER() macro for CHM decompression
  (CVE-2018-14682)
* Out-of-bounds write in mspack/cab.h (CVE-2018-18584)
* chmd_read_headers() fails to reject filenames containing NULL bytes
  (CVE-2018-18585)