Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 21 Aug 2018 11:21:15 -0400
From: Alex Gaynor <alex.gaynor@...il.com>
To: oss-security@...ts.openwall.com
Subject: Re: Re: More Ghostscript Issues: Should we disable PS
 coders in policy.xml by default?

A small note. Both ImageMagick and GraphicsMagick process various file
formats that can nest a different image file inside of them. These are very
frequently implemented with a call to ReadImage(), with no checking that
it's the expected file format. (As a result, the fuzzer finds various
impressive chains, with sometimes 3 different image formats nested inside
of each other).

The conclusion of this is that people _must not_ attempt to do their own
format detection and then pass the data to IM/GM, because this can be
bypassed with nested formats. It's imperative that GS truly be disabled
with either policy.xml or by uninstall GS.

Alex

On Tue, Aug 21, 2018 at 11:01 AM Bob Friesenhahn <
bfriesen@...ple.dallas.tx.us> wrote:

> On Tue, 21 Aug 2018, Tavis Ormandy wrote:
> >
> > I think those thumbnails should be disabled, but you've probably noticed
> I
> > think everything related to untrusted ghostscript should be disabled :-)
>
> I have posted to the GraphicsMagick Announcements mailing list
> regarding your findings (with a link to this list) and suggested that
> a fool-proof solution is that Ghostscript should be uninstalled.
>
> Uninstalling Ghostscript entirely might cause software using libgs to
> not execute at all unless a stub library is put in its place.
>
> Dependencies on Ghostscript are much larger than one would initially
> think due to Postscript being the traditional output from Unix
> software for "printing" and thus it is used as an intermediate format
> in order to convert between formats.  EPS content is also embedded in
> some other formats.
>
> Bob
> --
> Bob Friesenhahn
> bfriesen@...ple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
> GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
>


-- 
All that is necessary for evil to succeed is for good people to do nothing.

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.