ghostscript: NULL pointer dereference in compose_group_nonknockout_nonblend_isolated_allmask_common() in base/gxblend.c could result in a DoS

A null pointer dereference vulnerability in composegroupnonknockoutnonblendisolatedallmaskcommon in base/gxblend.c of Artifex Software GhostScript v9.50 allows a remote attacker to cause a denial of service via a crafted PDF file. This is fixed in v9.51...