Re: Re: More Ghostscript Issues: Should we disable PS coders in policy.xml by default?

[Stuart Gathman <stuart () gathman org>]

On 09/05/2018 03:01 PM, Perry E. Metzger wrote:
> On Wed, 5 Sep 2018 11:02:48 -0700 Tavis Ormandy <taviso () google com>
> wrote:
> > I would like to re-emphasize that while Ghostscript is very capable
> > and mature software, I consider the -dSAFER sandbox to be a fragile
> > security boundary and that we should consider deprecating (or
> > minimizing the use of) untrusted postscript.
> I haven't been following the bugs in depth (just noticing the
> continuous stream of them arriving), but is the issue security flaws
> in just -dSAFER or is it overall security bugs? If it's the former,
> given how few things actually need any of the features past what
> -dSAFER offers, perhaps compiling the code by default without any such
> capabilities would work well? You can't run what isn't there.
Postscript is a general purpose programming language.  It can do
anything to your system that a C or Python program could.  The SAFER
sandbox was supposed to be able to prevent untrusted postscript code
from doing serious damage.  But this series of bugs shows that the
sandbox is very flawed, and running untrusted postscript relying only on
the SAFER sandbox is a very bad idea.

What I need to study, is whether random PDF files from the internet (as
opposed to general postscript) are therefore malware vectors.  I thought
that PDF used a restricted subset of operations that "rendered" it not a
general purpose language and therefore "safe".   But if SAFER was the
implementation of that restricted subset, then all internet PDFs are
suspect.