Ghostscript -- Security bypass vulnerability

Cedric Buissart (Red Hat) reports:

It was found that the superexec operator was available in the
internal dictionary in ghostscript before 9.27. A specially crafted
PostScript file could use this flaw in order to, for example, have
access to the file system outside of the constrains imposed by
-dSAFER.

It was found that the forceput operator could be extracted from
the DefineResource method in ghostscript before 9.27. A specially
crafted PostScript file could use this flaw in order to, for
example, have access to the file system outside of the constrains
imposed by -dSAFER.