Friday, February 19, 2021

Asterisk Project Security Advisory - AST-2021-002

               Asterisk Project Security Advisory - AST-2021-002

Product Asterisk
Summary Remote crash possible when negotiating T.38
Nature of Advisory Denial of service
Susceptibility Remote authenticated sessions
Severity Minor
Exploits Known No
Reported On December 8, 2020
Reported By Gregory Massel
Posted On
Last Updated On February 5, 2021
Advisory Contact kharwell AT sangoma DOT com
CVE Name CVE-2021-26717

Description When re-negotiating for T.38 if the initial remote
response was delayed just enough Asterisk would send
both audio and T.38 in the SDP. If this happened, and
the remote responded with a declined T.38 stream then
Asterisk would crash.
Modules Affected res_pjsip_session.c, res_pjsip_t38.c

Resolution When re-negotiating for T.38, and a delay occurs Asterisk
now sends SDP only for the expected T.38 stream. A check was
also put in place to ensure an active T.38 media stream is
active within Asterisk when attempting to change state for

Affected Versions
Product Release Series Introduced
Asterisk Open Source 16.x 16.15.0
Asterisk Open Source 17.x 17.9.0
Asterisk Open Source 18.x 18.1.0
Certified Asterisk 16.8 16.8-cert4

Corrected In
Product Release
Asterisk Open Source 16.16.1, 17.9.2, 18.2.1
Certified Asterisk 16.8-cert6

Patch URL Revision Asterisk
16 Asterisk
17 Asterisk
18 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This document may be superseded by later versions; if so, the latest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 and

Revision History
Date Editor Revisions Made
February 1, 2021 Kevin Harwell Initial revision

Asterisk Project Security Advisory - AST-2021-002
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