Univention Corporate Server 4.2 erratum 576 (extended maintenance)

This update addresses the following issues:
* heap-based buffer over-read of size 8 in jas_image_depalettize in
  libjasper/base/jas_image.c (CVE-2018-19541)
* access violation in jas_image_readcmpt in libjasper/base/jas_image.c
  (CVE-2018-19539)
* DoS when converting to jp2 (CVE-2018-20584)
* heap-based buffer overflow of size 1 in jas_icctxtdesc_input in
  libjasper/base/jas_icc.c (CVE-2018-19540)
* invalid access in jp2_decode in libjasper/jp2/jp2_dec.c (CVE-2018-19542)
* memory leak in jas_malloc.c when called from jpc_unk_getparms in jpc_cs.c
  (CVE-2018-19139)
* NULL pointer dereference in ras_putdatastd function (CVE-2018-18873)
* memory leak in base/jas_malloc.c in libjasper.a (CVE-2018-20622)
* heap-based buffer over-read in jp2_encode in jp2/jp2_enc.c (CVE-2018-20570)