CVE-2018-16509

Impact:
Important
Public Date:
2018-08-21
Bugzilla:
1619748: CVE-2018-16509 ghostscript: /invalidaccess bypass after failed restore (699654)
It was discovered that the ghostscript /invalidaccess checks fail under certain conditions. An attacker could possibly exploit this to bypass the -dSAFER protection and, for example, execute arbitrary shell commands via a specially crafted PostScript document.

Find out more about CVE-2018-16509 from the MITRE CVE dictionary dictionary and NIST NVD.

Statement

This issue did affect the versions of ghostscript as shipped with Red Hat Enterprise Linux 5, 6, and 7.

Red Hat Enterprise Linux 5 is now in Extended Life Phase of the support and maintenance life cycle. This issue is not currently planned to be addressed in future updates. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.

CVSS v3 metrics

CVSS3 Base Score 7.3
CVSS3 Base Metrics CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Low
Integrity Impact Low
Availability Impact Low

Red Hat Security Errata

Platform Errata Release Date
Red Hat Enterprise Linux 7 (ghostscript) RHSA-2018:2918 2018-10-16
Red Hat Enterprise Linux 6 (ghostscript) RHSA-2018:3760 2018-12-03
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Acknowledgements

Red Hat would like to thank Tavis Ormandy (Google Project Zero) for reporting this issue.

Mitigation

* ImageMagick relies on ghostscript when processing certain files formats. Thus, ImageMagick can be used as an attack vector. In order to prevent ImageMagick from processing those files on Red Hat Enterprise Linux 6 and 7, you can disable the use of ghostscript and the processing of PS, EPS, PDF, and XPS file formats in ImageMagick's security policy by opening /etc/ImageMagick/policy.xml and adding the following lines to the "<policymap>" section of the file:

<policy domain="coder" rights="none" pattern="PS" />
<policy domain="coder" rights="none" pattern="EPS" />
<policy domain="coder" rights="none" pattern="PDF" />
<policy domain="coder" rights="none" pattern="XPS" />
<policy domain="delegate" rights="none" pattern="gs" />

* Additionally, this issue can be triggered when processing files in order to generate thumbnails, for example when browsing a folder containing a malicious PostScript file in Nautilus. To prevent this, remove or rename the "/usr/bin/evince-thumbnailer" executable.
In Red Hat Enterprise Linux v.7.6 and above, the thumbnailing is done in a sandbox.

* It is possible to run PDF/PS viewers, such as evince and okular, in a SELinux sandbox using the `sandbox` command from the policycoreutils-sandbox package :
$ sandbox -X evince <untrusted-file.pdf>
The sandbox will prevent an attacker to make modifications on the file system.

External References

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