Bug 1892636 (CVE-2020-14383)

Summary:	CVE-2020-14383 samba: An authenticated user can crash the DCE/RPC DNS with easily crafted records
Product:	[Other] Security Response	Reporter:	Huzaifa S. Sidhpurwala <huzaifas>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED NOTABUG	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	abokovoy, anoopcs, asn, gdeschner, hvyas, iboukris, iboukris, jarrpa, jstephen, lmohanty, madam, puebele, rhs-smb, sbose, ssorce
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	samba 4.11.15, samba 4.12.9, samba 4.13.1	Doc Type:	If docs needed, set a value
Doc Text:	A flaw was found in Samba's DNS server. This flaw allows an authenticated user to crash the RPC server. The RPC server, which also serves protocols other than the DNS server, is restarted after a short delay, however, an authenticated non-administrative attacker can cause a crash as soon as it returns. The Samba DNS server continues to operate, but many RPC services do not. The highest threat from this vulnerability is system availability.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2020-12-24 07:02:03 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:	1892638, 1892639, 1892640
Bug Blocks:	1891686

Description Huzaifa S. Sidhpurwala 2020-10-29 11:16:11 UTC

As per upstream advisory:

Some DNS records (such as MX and NS records) usually contain data in the additional section. Samba's dnsserver RPC pipe (which is an administrative interface not used in the DNS server itself) made an error in handling the case where there are no records present: instead of noticing the lack of records, it dereferenced uninitialised memory, causing the RPC server to crash. This RPC server, which also serves protocols other than dnsserver, will be restarted after a short delay,
but it is easy for an authenticated non-admin attacker to crash it again as soon as it returns. The Samba DNS server itself will continue to operate, but many RPC services will not.

Comment 1 Huzaifa S. Sidhpurwala 2020-10-29 11:16:20 UTC

Acknowledgments:

Name: the Samba project
Upstream: Francis Brosnan Blázquez (ASPL.es)

Comment 2 Huzaifa S. Sidhpurwala 2020-10-29 11:16:26 UTC

External References:

https://www.samba.org/samba/security/CVE-2020-14383.html

Comment 3 Huzaifa S. Sidhpurwala 2020-10-29 11:16:36 UTC

Mitigation:

The dnsserver task can be stopped by setting

 'dcerpc endpoint servers = -dnsserver'

in the smb.conf and restarting Samba.

Comment 4 Huzaifa S. Sidhpurwala 2020-10-29 11:18:41 UTC

Created samba tracking bugs for this issue:

Affects: fedora-all [bug 1892640]

Comment 7 Hardik Vyas 2020-11-06 12:39:09 UTC

Upstream patches:

samba-4.13.1:
https://git.samba.org/?p=samba.git;a=commit;h=4cbf95e731b39b2dbfec02f33fd6b195d0b0f7a8
https://git.samba.org/?p=samba.git;a=commit;h=862d6fb6f3235126c96683516c12a284bcf84901

samba-4.12.9:
https://git.samba.org/?p=samba.git;a=commit;h=2d7d1dff7d20d5b06ff50452e7f714af9f6a109e
https://git.samba.org/?p=samba.git;a=commit;h=425c31a599bb96c7d01273fc50b682bc42dbed57

samba-4.11.15:
https://git.samba.org/?p=samba.git;a=commit;h=2632e8ebae826a7305fe7d3948ee28b77d2ffbc0
https://git.samba.org/?p=samba.git;a=commit;h=8e09649351e9e8143b4bd0b76bcbd2cfb4d2f281

Comment 16 Huzaifa S. Sidhpurwala 2020-12-24 07:01:13 UTC

Statement:

This issue does not affect the version of samba as shipped with Red Hat Enterprise Linux 6, 7, 8 and Red Hat Gluster Storage 3 as it does not include support for Active Directory Domain Controller.