Univention Corporate Server 4.3 erratum 455 (security)

This update addresses the following issues:
* Due to the way rename() across filesystems is implemented, it is possible
  that file being renamed is briefly available with wrong permissions while
  the rename is ongoing, thus enabling unauthorized users to access the data.
  (CVE-2019-9637)
* Uninitialized read in exif_process_IFD_in_MAKERNOTE because of mishandling
  the maker_note->offset relationship to value_len. (CVE-2019-9638)
* Uninitialized read in exif_process_IFD_in_MAKERNOTE because of mishandling
  the data_len variable. (CVE-2019-9639)
* Invalid Read in exif_process_SOFn. (CVE-2019-9640)
* Uninitialized read in exif_process_IFD_in_TIFF. (CVE-2019-9641)