Univention Corporate Server 4.2 erratum 569 (extended maintenance)

This update addresses the following issues:
* libarchive contains a CWE-415: Double Free vulnerability in RAR decoder -
  libarchive/archive_read_support_format_rar.c, parse_codes(),
  realloc(rar->lzss.window, new_size) with new_size = 0 that can result in
  Crash/DoS. This attack appears to be exploitable only if the victim opens
  a specially crafted RAR archive. (CVE-2018-1000877)
* libarchive version contains a CWE-416: Use After Free vulnerability in RAR
  decoder - libarchive/archive_read_support_format_rar.c that can result in
  Crash/DoS - it is unknown if RCE is possible. This attack appears to be
  exploitable only if the victim opens a specially crafted RAR archive.
  (CVE-2018-1000878)