ESB-2018.2631 - [UNIX/Linux] ghostscript: Multiple vulnerabilities 2018-09-05

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===========================================================================
             AUSCERT External Security Bulletin Redistribution

                               ESB-2018.2631
                  Ghostscript -- arbitrary code execution
                             5 September 2018

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           ghostscript
Publisher:         CERT/CC
Operating System:  UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Execute Arbitrary Code/Commands -- Remote/Unauthenticated
                   Denial of Service               -- Remote/Unauthenticated
Resolution:        Mitigation

Original Bulletin: 
   https://www.kb.cert.org/vuls/id/332928

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Vulnerability Note VU#332928

Ghostscript contains multiple -dSAFER sandbox bypass vulnerabilities

Original Release date: 21 Aug 2018 | Last revised: 04 Sep 2018

Overview

Ghostscript contains multiple -dSAFER sandbox bypass vulnerabilities, which may
allow a remote, unauthenticated attacker to execute arbitrary commands on a
vulnerable system.

Description

Ghostscript contains an optional -dSAFER option, which is supposed to prevent
unsafe PostScript operations. Multiple PostScript operations bypass the
protections provided by -dSAFER, which can allow an attacker to execute
arbitrary commands with arbitrary arguments. This vulnerability can also be
exploited in applications that leverage Ghostscript, such as ImageMagick,
GraphicsMagick, evince, Okular, Nautilus, and others.

Exploit code for this vulnerability is publicly available.


Impact

By causing Ghostscript or a program that leverages Ghostscript to parse a
specially-crafted file, a remote, unauthenticated attacker may be able to
execute arbitrary commands with the privileges of the Ghostscript code. This
action may be triggered with actions as simple as downloading a file from a
website.


Solution

The CERT/CC is currently unaware of a practical solution to this problem.
Please consider the following workarounds:

Disable PS, EPS, PDF, and XPS coders in ImageMagick policy.xml

ImageMagick uses Ghostscript by default to process PostScript content.
ImageMagick can be controlled via the policy.xml security policy  to disable
the processing of PS, EPS, PDF, and XPS content. For example, this can be done
by adding these lines to the <policymap> section of the /etc/ImageMagick/
policy.xml file on a RedHat system:

    <policy domain="coder" rights="none" pattern="PS" />
    <policy domain="coder" rights="none" pattern="PS2" />
    <policy domain="coder" rights="none" pattern="PS3" />
    <policy domain="coder" rights="none" pattern="EPS" />
    <policy domain="coder" rights="none" pattern="PDF" />
    <policy domain="coder" rights="none" pattern="XPS" />


Check with your vendor for the proper location of this file on your platform.
Note that this workaround only mitigates the ImageMagick attack vector to
Ghostscript.

Remove Ghostscript

Because of the number of different attack vectors to get to Ghostscript and the
public availability of exploit code, the most effective protection for this
vulnerability is to remove Ghostscript from your system until a fixed version
is available.

Patch Ghostscript

Artifex software has made the following patches available for Ghostscript:

http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=b575e1ec
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=8e9ce501
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=241d9111
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=c432131c
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=e01e77a3
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=0edd3d6c
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=a054156d
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=0d390118
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=c3476dde
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=b326a716
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=78911a01
http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=5516c614


Vendor Information (Learn More)

        Vendor            Status    Date Notified Date Updated
Artifex Software, Inc. Affected     24 Aug 2018   24 Aug 2018
CentOS                 Affected     21 Aug 2018   22 Aug 2018
Debian GNU/Linux       Affected     21 Aug 2018   22 Aug 2018
Fedora Project         Affected     21 Aug 2018   22 Aug 2018
FreeBSD Project        Affected     21 Aug 2018   22 Aug 2018
Gentoo Linux           Affected     21 Aug 2018   22 Aug 2018
ImageMagick            Affected     24 Aug 2018   24 Aug 2018
Red Hat, Inc.          Affected     21 Aug 2018   21 Aug 2018
SUSE Linux             Affected     21 Aug 2018   22 Aug 2018
Synology               Affected     -             23 Aug 2018
Ubuntu                 Affected     21 Aug 2018   21 Aug 2018
Apple                  Not Affected 21 Aug 2018   27 Aug 2018
CoreOS                 Not Affected 21 Aug 2018   21 Aug 2018
Arch Linux             Unknown      21 Aug 2018   21 Aug 2018
Arista Networks, Inc.  Unknown      21 Aug 2018   21 Aug 2018

If you are a vendor and your product is affected, let us know.View More &raquo


CVSS Metrics (Learn More)

    Group     Score             Vector
Base          7.5   AV:N/AC:L/Au:N/C:P/I:P/A:P
Temporal      6.8   E:F/RL:W/RC:C
Environmental 6.8   CDP:ND/TD:ND/CR:ND/IR:ND/AR:ND

References

  o http://openwall.com/lists/oss-security/2018/08/21/2
  o https://bugs.chromium.org/p/project-zero/issues/detail-id=1640
  o https://www.imagemagick.org/script/security-policy.php
  o https://www.imagemagick.org/script/resources.php
  o https://www.ghostscript.com/doc/current/Use.htm#Safer
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=b575e1ec
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=8e9ce501
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=241d9111
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=c432131c
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=e01e77a3
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=e01e77a3
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=0edd3d6c
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=a054156d
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=0d390118
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=c3476dde
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=b326a716
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=78911a01
  o http://git.ghostscript.com/-p=ghostpdl.git;a=commitdiff;h=5516c614

Credit

This vulnerability was publicly disclosed by Tavis Ormandy.

This document was written by Will Dormann.

Other Information

  o CVE IDs: Unknown
  o Date Public: 21 Feb 2018
  o Date First Published: 21 Aug 2018
  o Date Last Updated: 04 Sep 2018
  o Document Revision: 44

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