Asterisk Project Security Advisory – AST-2019-003

Asterisk Project Security Advisory – AST-2019-003

Product Asterisk
Summary Remote Crash Vulnerability in chan_sip channel
Nature of Advisory Denial of Service
Susceptibility Remote Unauthenticated Sessions
Severity Minor
Exploits Known No
Reported On June 28, 2019
Reported By Francesco Castellano
Posted On July 1, 2019
Last Updated On July 2, 2019
Advisory Contact Jcolp AT sangoma DOT com
CVE Name CVE-2019-13161

Description When T.38 faxing is done in Asterisk a T.38 reinvite may be
sent to an endpoint to switch it to T.38. If the endpoint
responds with an improperly formatted SDP answer including
both a T.38 UDPTL stream and an audio or video stream
containing only codecs not allowed on the SIP peer or user
a crash will occur. The code incorrectly assumes that there
will be at least one common codec when T.38 is also in the
SDP answer.

This requires Asterisk to initiate a T.38 reinvite which is
only done when executing the ReceiveFax dialplan
application or performing T.38 passthrough where a remote
endpoint has requested T.38.

For versions of Asterisk 13 before 13.21.0 and Asterisk 15
before 15.4.0 the “preferred_codec_only” option must also
be set to “yes”. If set to “no” the crash will not occur.

Resolution If T.38 faxing is not required this functionality can be
disabled by ensuring the “t38pt_udptl” is set to “no” so a
T.38 reinvite is not possible.

If T.38 faxing is required then Asterisk should be upgraded
to a fixed version. The problem can also be limited in scope
by enabling T.38 faxing only for endpoints which actually
participate in fax.

Affected Versions
Product Release Series
Asterisk Open Source 13.x All releases
Asterisk Open Source 15.x All releases
Asterisk Open Source 16.x All releases
Certified Asterisk 13.21 All releases

Corrected In
Product Release
Asterisk Open Source 13.27.1
Asterisk Open Source 15.7.3
Asterisk Open Source 16.4.1
Certified Asterisk 13.21-cert4

SVN URL Revision Asterisk
13 Asterisk
15 Asterisk
16 Certified


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Revision History
Date Editor Revisions Made
July 1, 2019 Joshua Colp Initial revision

Asterisk Project Security Advisory – AST-2019-003
Copyright © 2019 Digium, Inc. All Rights Reserved.
Permission is hereby granted to distribute and publish this advisory in its
original, unaltered form.