Bug 1950506 (CVE-2021-3493)

Summary:	CVE-2021-3493 kernel: overlayfs file system caps privilege escalation
Product:	[Other] Security Response	Reporter:	Pedro Sampaio <psampaio>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	acaringi, adscvr, airlied, alciregi, bdettelb, bhu, blc, bmasney, brdeoliv, bskeggs, chwhite, crwood, dhoward, dvlasenk, fhrbata, fpacheco, hdegoede, hkrzesin, jarodwilson, jeremy, jforbes, jglisse, jlelli, jonathan, josef, jshortt, jstancek, jwboyer, kcarcia, kernel-maint, kernel-mgr, lgoncalv, linville, masami256, mchehab, mlangsdo, nmurray, ptalbert, qzhao, rvrbovsk, steved, tomckay, walters, wcosta, williams, wmealing
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:	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.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-04-28 07:18:25 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1950507

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