The xps_select_font_encoding function in xps/xpsfont.c in Artifex Ghostscript GhostXPS 9.21 allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) or possibly have unspecified other impact via a crafted document, related to the xps_encode_font_char_imp function.
https://security.gentoo.org/glsa/201811-12
http://www.securityfocus.com/bid/99990
http://git.ghostscript.com/?p=ghostpdl.git%3Ba=commit%3Bh=3ee55637480d5e319a5de0481b01c3346855cbc9