Bug 1607285 (CVE-2018-6553) - CVE-2018-6553 cups: AppArmor cupsd Sandbox Bypass Due to Use of Hard Links
Summary: CVE-2018-6553 cups: AppArmor cupsd Sandbox Bypass Due to Use of Hard Links
Keywords:
Status: CLOSED NOTABUG
Alias: CVE-2018-6553
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks: 1607292
TreeView+ depends on / blocked
 
Reported: 2018-07-23 08:12 UTC by Andrej Nemec
Modified: 2021-02-16 23:55 UTC (History)
12 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
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.
Clone Of:
Environment:
Last Closed: 2018-07-24 14:57:29 UTC
Embargoed:

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Description Andrej Nemec 2018-07-23 08:12:41 UTC 
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 13:01:27 UTC 
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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