Asterisk Project Security Advisory – AST-2019-008

Asterisk Project Security Advisory –

Product Asterisk
Summary Re-invite with T.38 and malformed SDP causes crash.
Nature of Advisory Remote Crash
Susceptibility Remote Authenticated Sessions
Severity Minor
Exploits Known No
Reported On November 07, 2019
Reported By Salah Ahmed
Posted On November 21, 2019
Last Updated On November 21, 2019
Advisory Contact bford AT sangoma DOT com
CVE Name CVE-2019-18976

Description If Asterisk receives a re-invite initiating T.38
faxing and has a port of 0 and no c line in the SDP, a
crash will occur.
Modules Affected res_pjsip_t38.c

Resolution If T.38 faxing is not needed, then the “t38_udptl”
configuration option in pjsip.conf can be set to “no” to
disable the functionality. This option automatically
defaults to “no” and would have to be manually turned on to
experience this crash.

If T.38 faxing is needed, then Asterisk should be upgraded
to a fixed version.

Affected Versions
Product Release
Asterisk Open Source 13.x All versions
Certified Asterisk 13.21 All versions

Corrected In
Product Release
Asterisk Open Source 13.29.2
Certified Asterisk 13.21-cert5

SVN URL Revision Asterisk 13 Certified


Asterisk Project Security Advisories are posted at

This document may be superseded by later versions; if so, the latest
version will be posted at

Revision History
Date Editor Revisions Made
November 12, 2019 Ben Ford Initial Revision
November 21, 2019 Ben Ford Added “Posted On” date

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