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.
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