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: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: abokovoy, anoopcs, asn, dkarpele, gdeschner, hvyas, iboukris, jrivera, jstephen, lmohanty, madam, pfilipen, puebele, rhs-smb, sbose, security-response-team, ssorce
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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:
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):


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:

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):