Bug 1397341 (CVE-2016-7429)

Summary: CVE-2016-7429 ntp: Attack on interface selection
Product: [Other] Security Response Reporter: Adam Mariš <amaris>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: apmukher, keyur.three0, mlichvar, sardella, slawomir, woodard, yozone
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: ntp-4.2.8p9 Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the way ntpd running on a host with multiple network interfaces handled certain server responses. A remote attacker could use this flaw which would cause ntpd to not synchronize with the source.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2017-02-06 06:50:25 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: 1397351, 1411642, 1411643, 1411644, 1411645    
Bug Blocks: 1397349    

Description Adam Mariš 2016-11-22 10:50:29 UTC 
When ntpd receives a server response on a socket that corresponds to a different interface than was used for the request, the peer structure is updated to use the interface for new requests. If ntpd is running on a host with multiple interfaces in separate networks and the operating system doesn't check source address in received packets (e.g. rp_filter on Linux is set to 0), an attacker that knows the address of the source can send a packet with spoofed source address which will cause ntpd to select wrong interface for the source and prevent it from sending new requests until the list of interfaces is refreshed, which happens on routing changes or every 5 minutes by default. If the attack is repeated often enough (once per second), ntpd will not be able to synchronize with the source.

External References:

http://support.ntp.org/bin/view/Main/NtpBug3072
Comment 1 Adam Mariš 2016-11-22 11:09:29 UTC 
Created ntp tracking bugs for this issue:

Affects: fedora-all [bug 1397351]
Comment 2 Huzaifa S. Sidhpurwala 2016-12-14 08:14:30 UTC 
Mitigation:

If you are going to configure your OS to disable source address checks, also configure your firewall configuration to control what interfaces can receive packets from what networks.
Comment 4 Keyur Pujara 2017-01-16 11:30:01 UTC 
Is an RPM released with fix for this. I haven't seen one @ http://mirror.centos.org. 

If not released, what is ETA for same?

Thanks, Keyur
Comment 5 errata-xmlrpc 2017-02-06 06:17:34 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 6
  Red Hat Enterprise Linux 7

Via RHSA-2017:0252 https://rhn.redhat.com/errata/RHSA-2017-0252.html