The pdf14_pop_transparency_group function in base/gdevp14.c in the PDF Transparency module in Artifex Software, Inc. Ghostscript 9.20 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a crafted file.
http://git.ghostscript.com/?p=ghostpdl.git%3Ba=commit%3Bh=d621292fb2c8157d9899dcd83fd04dd250e30fe4