Bug 1691518 (CVE-2019-3880)

Summary:	CVE-2019-3880 samba: save registry file outside share as unprivileged user
Product:	[Other] Security Response	Reporter:	Laura Pardo <lpardo>
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, bmcclain, dblechte, dfediuck, eedri, gdeschner, jarrpa, jlyle, jstephen, lmohanty, madam, mgoldboi, michal.skrivanek, rhs-smb, rwagner, sankarshan, sbonazzo, sbose, security-response-team, sherold, sisharma, ssorce, vbellur, yozone, yturgema
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	samba 4.8.11, samba 4.9.6, samba 4.10.2	Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in the way samba implemented an RPC endpoint emulating the Windows registry service API. An unprivileged attacker could use this flaw to create a new registry hive file anywhere they have unix permissions which could lead to creation of a new file in the Samba share.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-07-30 13:18:30 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:	1696524, 1696525, 1696577, 1697717
Bug Blocks:	1691522

Description Laura Pardo 2019-03-21 19:42:44 UTC

As per samba upstream advisory:

Samba contains an RPC endpoint emulating the Windows registry service API. One of the requests, "winreg_SaveKey", is susceptible to a path/symlink traversal vulnerability. Unprivileged users can use it to create a new registry hive file anywhere they have unix permissions to create a new file within a Samba share. If they are able to create symlinks on a Samba share, they can create a new registry hive file anywhere they have write access, even outside a Samba share definition.

Note - existing share restrictions such as "read only" or share ACLs do *not* prevent new registry hive files being written to the filesystem. A file may be written under any share definition wherever the user has unix permissions to create a file.

Existing files cannot be overwritten using this vulnerability, only new registry hive files can be created, however the presence of existing files with a specific name can be detected.

Samba writes or detects the file as the authenticated user, not as root.

Comment 1 Laura Pardo 2019-03-21 19:45:14 UTC

Acknowledgments:

Name: Michael Hanselmann

Comment 2 Dave Baker 2019-03-27 20:05:19 UTC

openshift-online-3 does not provision samba endpoints.

Comment 5 Huzaifa S. Sidhpurwala 2019-04-05 06:00:45 UTC

Note: 

This affects not only Linux <> Windows configurations but may also affect Linux <> Linux configurations using Samba as RPC endpoints. (since winreg_SaveKey RPC call is also implemented on the client side)

Comment 7 Huzaifa S. Sidhpurwala 2019-04-05 06:07:45 UTC

Mitigation:

Either turn off SMB1 by setting the global parameter:
'min protocol = SMB2'
or if SMB1 is required turn off unix extensions by setting the global parameter:
'unix extensions = no'
in the smb.conf file.

Comment 11 Doran Moppert 2019-04-09 04:04:48 UTC

External References:

https://www.samba.org/samba/security/CVE-2019-3880.html

Comment 12 Doran Moppert 2019-04-09 04:05:08 UTC

Created samba tracking bugs for this issue:

Affects: fedora-all [bug 1697717]

Comment 13 Hardik Vyas 2019-04-09 06:04:04 UTC

Statement:

This issue affects the version of samba shipped with Red Hat Gluster Storage 3, as it contains the vulnerable functionality.

Comment 15 errata-xmlrpc 2019-07-30 10:04:18 UTC

This issue has been addressed in the following products:

  Red Hat Gluster Storage 3.4 for RHEL 7

Via RHSA-2019:1966 https://access.redhat.com/errata/RHSA-2019:1966

Comment 16 errata-xmlrpc 2019-07-30 10:22:12 UTC

This issue has been addressed in the following products:

  Red Hat Gluster Storage 3.4 for RHEL 6

Via RHSA-2019:1967 https://access.redhat.com/errata/RHSA-2019:1967

Comment 17 Product Security DevOps Team 2019-07-30 13:18:30 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-2019-3880

Comment 18 errata-xmlrpc 2019-08-06 12:13:49 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2019:2099 https://access.redhat.com/errata/RHSA-2019:2099

Comment 19 errata-xmlrpc 2019-11-05 21:14:25 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2019:3582 https://access.redhat.com/errata/RHSA-2019:3582