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Date: Thu, 23 Aug 2018 15:33:33 +0200
From: Leonardo Taccari <iamleot@...il.com>
To: oss-security@...ts.openwall.com
Subject: Re: Re: More Ghostscript Issues: Should we disable PS coders in policy.xml by default?

Hello Bob,

Bob Friesenhahn writes:
> You are missing something.  While they are unlikely to be triggered by 
> default (but still could be triggered by an attacker with sufficient 
> control), testing shows that
>
>    convert -verbose PS2:file.ps outfile.png
>    convert -verbose file.ps2 outfile.png
>    convert -verbose PS3:file.ps outfile.png
>    convert -verbose file.ps3 outfile.png
>
> does in fact invoke Ghostscript.

Whoops, I stand corrected, sorry for the incorrect information!
(at least when invoking them with the `PS2:' or `PS3:' prefixes,
anyway, yes, both PS2 and PS3 policy rules are worth to be added
as well).

(Regarding the `file.ps2' and `file.ps3' examples without `PS2:' or
`PS3:' prefixes according `convert -debug Policy -log "%e"' it seems
that they ends up as:

 Domain: Coder; rights=Read; pattern="PS" ...

...so should be blocked by the workaround described in
VU#332928. But please correct me if I'm wrong.)

JFTR, not related to PS2 and PS3 but also a possible ghostcript
consumer: EPT seems to ends up as `pattern="PS"' too (unlike PS2
and PS3).


Thank you!

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