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Bug 1607285 - (CVE-2018-6553) CVE-2018-6553 cups: AppArmor cupsd Sandbox Bypass Due to Use of Hard Links
CVE-2018-6553 cups: AppArmor cupsd Sandbox Bypass Due to Use of Hard Links
Status: CLOSED NOTABUG
Product: Security Response
Classification: Other
Component: vulnerability (Show other bugs)
unspecified
All Linux
high Severity high
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Assigned To: Red Hat Product Security
impact=important,public=20180509,repo...
: Security
Depends On:
Blocks: 1607292
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Reported: 2018-07-23 04:12 EDT by Andrej Nemec
Modified: 2018-08-28 10:11 EDT (History)
12 users (show)

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Doc Text:
An AppArmor sandbox bypass has been discovered in cups due to the use of hard links which are not covered by the AppArmor profile. An attacker could use the hard link, if it exists, to execute the referenced backend without sandbox restrictions.
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Last Closed: 2018-07-24 10:57:29 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description Andrej Nemec 2018-07-23 04:12:41 EDT 
It is possible to bypass the AppArmor cupsd sandbox by invoking the dnssd backend using an alternate name that has been hard linked to dnssd.  Both Debian and Ubuntu use AppArmor and shipped the mdns backend in this manner, in contrast to macOS and other systems that use symbolic links.  Invoking the mdns backend causes the AppArmor profile to treat the backend as 3rd party, removing sandbox restrictions.

References:

https://blog.gdssecurity.com/labs/2018/7/11/cups-local-privilege-escalation-and-sandbox-escapes.html

Upstream patch:

https://github.com/apple/cups/commit/d47f6aec436e0e9df6554436e391471097686ecc
Comment 1 Riccardo Schirone 2018-08-28 09:01:27 EDT 
Statement:

This issue did not affect the versions of cups as shipped with Red Hat Enterprise Linux as they did not include support for AppArmor.
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