Bug 2009673 (CVE-2021-20316)

Summary:	CVE-2021-20316 samba: Symlink race error can allow metadata read and modify outside of the exported share
Product:	[Other] Security Response	Reporter:	Huzaifa S. Sidhpurwala <huzaifas>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	abokovoy, anoopcs, asn, dkarpele, gdeschner, hvyas, iboukris, jarrpa, jstephen, lmohanty, madam, pfilipen, puebele, rhs-smb, sbose, security-response-team, ssorce
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	samba 4.15.0	Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in the way Samba handled file/directory metadata. This flaw allows an authenticated attacker with permissions to read or modify share metadata, to perform this operation outside of the share.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2022-05-12 02:45:17 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:	2039034, 2039153, 2039154, 2046269
Bug Blocks:	2009675

Description Huzaifa S. Sidhpurwala 2021-10-01 09:13:41 UTC

As per upstream report: 

All versions of Samba prior to 4.15.0 are vulnerable to a malicious client using an SMB1 or NFS symlink race to allow filesystem metadata to be accessed in an area of the server file system not exported under the share definition. Note that SMB1 has to be enabled, or the share also available via NFS in order for this attack to succeed.

Clients that have write access to the exported part of the file system under a share via SMB1 unix extensions or NFS can create symlinks that can race the server by renaming an existing path and then replacing it with a symlink. If the client wins the race it can cause the server to read or modify file or directory metadata on the symlink target.

The authenticated user must have permissions to read or modify the metadata of the target of the symlink in order to perform the operation outside of the share.

Filesystem metadata includes such attributes as timestamps, extended attributes, permissions, and ownership.

Comment 1 Huzaifa S. Sidhpurwala 2021-10-04 03:29:39 UTC

Upstream bug (currently private):

https://bugzilla.samba.org/show_bug.cgi?id=14842

Comment 2 Guilherme de Almeida Suckevicz 2022-01-10 18:47:34 UTC

Created samba tracking bugs for this issue:

Affects: fedora-all [bug 2039034]

Comment 5 Tomas Hoger 2022-05-06 09:21:33 UTC

Upstream advisory:
https://www.samba.org/samba/security/CVE-2021-20316.html

Comment 6 errata-xmlrpc 2022-05-10 04:15:59 UTC

This issue has been addressed in the following products:

  Red Hat Gluster Storage 3.5 for RHEL 8

Via RHSA-2022:1756 https://access.redhat.com/errata/RHSA-2022:1756

Comment 7 errata-xmlrpc 2022-05-10 15:15:28 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2022:2074 https://access.redhat.com/errata/RHSA-2022:2074

Comment 8 Product Security DevOps Team 2022-05-12 02:45:14 UTC

This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2021-20316