Product

Asterisk

Summary

Media takeover in RTP stack

Nature of Advisory

Unauthorized data disclosure

Susceptibility

Remote Unauthenticated Sessions

Severity

Critical

Exploits Known

No

Reported On

May 17, 2017

Reported By

Klaus-Peter Junghanns

Posted On

August 31, 2017

Last Updated On

August 31, 2017

Advisory Contact

Joshua Colp <jcolp AT digium DOT com>

CVE Name

CVE-2017-14099

Description

The “strictrtp” option in rtp.conf enables a feature of the RTP stack that learns the source address of media for a session and drops any packets that do not originate from the expected address. This option is enabled by default in Asterisk 11 and above.

The “nat” and “rtp_symmetric” options for chan_sip and chan_pjsip respectively enable symmetric RTP support in the RTP stack. This uses the source address of incoming media as the target address of any sent media. This option is not enabled by default but is commonly enabled to handle devices behind NAT.

A change was made to the strict RTP support in the RTP stack to better tolerate late media when a reinvite occurs. When combined with the symmetric RTP support this introduced an avenue where media could be hijacked. Instead of only learning a new address when expected the new code allowed a new source address to be learned at all times.

If a flood of RTP traffic was received the strict RTP support would allow the new address to provide media and with symmetric RTP enabled outgoing traffic would be sent to this new address, allowing the media to be hijacked. Provided the attacker continued to send traffic they would continue to receive traffic as well.

Resolution

The RTP stack will now only learn a new source address if it has been told to expect the address to change. The RTCP support has now also been updated to drop RTCP reports that are not regarding the RTP session currently in progress. The strict RTP learning progress has also been improved to guard against a flood of RTP packets attempting to take over the media stream.

Affected Versions

Product

Release Series

Asterisk Open Source

11.x

11.4.0

Asterisk Open Source

13.x

All Releases

Asterisk Open Source

14.x

All Releases

Certified Asterisk

11.6

All Releases

Certified Asterisk

13.13

All Releases

Corrected In

Product

Release

Asterisk Open Source

11.25.2, 13.17.1, 14.6.1

Certified Asterisk

11.6-cert17, 13.13-cert5

Patches

SVN URL

Revision

http://downloads.asterisk.org/pub/security/AST-2017-005-11.diff

Asterisk 11

http://downloads.asterisk.org/pub/security/AST-2017-005-13.diff

Asterisk 13

http://downloads.asterisk.org/pub/security/AST-2017-005-14.diff

Asterisk 14

http://downloads.asterisk.org/pub/security/AST-2017-005-11.6.diff

Certified Asterisk 11.6

http://downloads.asterisk.org/pub/security/AST-2017-005-13.13.diff

Certified Asterisk 13.13

Links

https://issues.asterisk.org/jira/browse/ASTERISK-27013

Asterisk Project Security Advisories are posted at http://www.asterisk.org/security

This document may be superseded by later versions; if so, the latest version will be posted at http://downloads.digium.com/pub/security/AST-2017-005.pdf and http://downloads.digium.com/pub/security/AST-2017-005.html

Revision History

Date

Editor

Revisions Made

May 30, 2017

Joshua Colp

Initial Revision

August 31, 2017

Kevin Harwell

Updated for CVE