Univention Corporate Server 4.3 erratum 592 (security)

This update addresses the following issues:
* Heap buffer overflow in function xif_process_IFD_TAG (CVE-2019-11034)
* Heap buffer overflow in function exif_iif_add_value (CVE-2019-11035)
* Buffer over-read in exif_process_IFD_TAG function leading to information
  disclosure (CVE-2019-11036)
* Information disclosure in function gdImageCreateFromXbm() (CVE-2019-11038)
* Out-of-bounds read due to integer overflow in function
  iconv_mime_decode_headers() (CVE-2019-11039)
* Information disclosure in function exif_read_data() leads to denial of
  service (CVE-2019-11040)
* Heap buffer over-read in exif_scan_thumbnail() (CVE-2019-11041)
* Heap buffer over-read in exif_process_user_comment() (CVE-2019-11042)