The PS Interpreter in Ghostscript 9.18 and 9.20 allows remote attackers to execute arbitrary code via crafted userparams.
https://security.gentoo.org/glsa/201702-31
https://bugs.ghostscript.com/show_bug.cgi?id=697178
http://www.securityfocus.com/bid/95332
http://www.openwall.com/lists/oss-security/2016/10/19/6