Bug 1300269 (CVE-2015-7977)

Summary:	CVE-2015-7977 ntp: restriction list NULL pointer dereference
Product:	[Other] Security Response	Reporter:	Martin Prpič <mprpic>
Component:	vulnerability	Assignee:	Red Hat Product Security <security-response-team>
Status:	CLOSED ERRATA	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	mlichvar, sardella, slawomir
Target Milestone:	---	Keywords:	Reopened, Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	ntp 4.2.8p6	Doc Type:	Bug Fix
Doc Text:	A NULL pointer dereference flaw was found in the way ntpd processed 'ntpdc reslist' commands that queried restriction lists with a large amount of entries. A remote attacker could potentially use this flaw to crash ntpd.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2016-11-06 04:14:31 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:	1300277, 1301972, 1317795
Bug Blocks:	1297474, 1323912

Description Martin Prpič 2016-01-20 11:42:32 UTC

A NULL pointer dereference flaw was found in the way ntpd processed 'ntpdc reslist' commands that queried restriction lists with a large amount of entries. A remote attacker could use this flaw to crash the ntpd process.

Upstream patch (which also addresses CVE-2015-7978):

https://github.com/ntp-project/ntp/commit/8a0c765f3c47633fa262356b0818788d1cf249b1

Comment 1 Martin Prpič 2016-01-20 11:51:01 UTC

External References:

http://support.ntp.org/bin/view/Main/SecurityNotice#January_2016_NTP_4_2_8p6_Securit
http://www.talosintel.com/reports/TALOS-2016-0074/

Comment 2 Martin Prpič 2016-01-20 12:01:57 UTC

Created ntp tracking bugs for this issue:

Affects: fedora-all [bug 1300277]

Comment 3 Martin Prpič 2016-01-21 14:09:20 UTC

To exploit this issue, the attacker has to rely on two factors:

* ntpd to be configured to receive mode 7 packets. By default on Red Hat Enterprise Linux, ntpd is configured to receive this packets only on localhost.

* the restriction list must contain a large number of entries (more than 500).

When the number of entries is large enough, the NULL pointer dereference is triggered and causes ntpd to crash.

Since the attacker has no way of influencing the size of the restriction list by adding more entries, it is quite unlikely to exploit this issue.

Having such a large number of restriction entries would also be an uncommon configuration since it would be more practical to restrict connecting clients via other means (e.g. iptables) should the system require it.

Statement:

This issue affects the versions of ntp as shipped with Red Hat Enterprise Linux 5, 6, and 7. Red Hat Product Security has rated this issue as having Moderate security impact. A future update may address this issue in Red Hat Enterprise Linux 6 and 7. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/.

Comment 4 Martin Prpič 2016-01-21 14:10:41 UTC

Mitigation:

Keep the number of restriction list entries in ntp.conf lower than 500.

Comment 6 Fedora Update System 2016-01-30 18:21:16 UTC

ntp-4.2.6p5-36.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.

Comment 7 Fedora Update System 2016-02-21 02:24:47 UTC

ntp-4.2.6p5-36.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.

Comment 9 errata-xmlrpc 2016-05-10 20:18:22 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6

Via RHSA-2016:0780 https://rhn.redhat.com/errata/RHSA-2016-0780.html

Comment 10 errata-xmlrpc 2016-11-03 19:33:26 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2016:2583 https://rhn.redhat.com/errata/RHSA-2016-2583.html