In Artifex Ghostscript 9.23 before 2018-08-24, a type confusion using the .shfill operator could be used by attackers able to supply crafted PostScript files to crash the interpreter or potentially execute code.
https://access.redhat.com/errata/RHSA-2018:3650
https://lists.debian.org/debian-lts-announce/2018/09/msg00015.html
https://security.gentoo.org/glsa/201811-12
https://support.f5.com/csp/article/K24803507?utm_source=f5support&%3Butm_medium=RSS