Bug 1950506 (CVE-2021-3493) - CVE-2021-3493 kernel: overlayfs file system caps privilege escalation
Summary: CVE-2021-3493 kernel: overlayfs file system caps privilege escalation
Keywords:
Status: CLOSED NOTABUG
Alias: CVE-2021-3493
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
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Depends On:
Blocks: 1950507
TreeView+ depends on / blocked
 
Reported: 2021-04-16 18:37 UTC by Pedro Sampaio
Modified: 2021-05-03 06:07 UTC (History)
46 users (show)

Fixed In Version:
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A flaw was found in the Linux kernel. The overlayfs stacking file system does not properly validate the application of file capabilities against user namespaces. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
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Environment:
Last Closed: 2021-04-28 07:18:25 UTC

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Description Pedro Sampaio 2021-04-16 18:37:24 UTC 
An independent security researcher reported  that the overlayfs stacking file system within the Linux kernel as used within Ubuntu did not properly validate the application of file capabilities against user namespaces.

This issue is not relevant to Red Hat Enterprise Linux kernels, as Ubuntu carries a patch to enable unprivileged overlayfs mounts. The combination of that patch and allowing unprivileged user namespaces by default in Ubuntu allows an unprivileged attacker to gain elevated privileges.
References:

https://www.openwall.com/lists/oss-security/2021/04/16/1
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