An asterisk security update has been released for Debian GNU/Linux 9 LTS to address a crash.

DLA 2729-1: asterisk security update

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Debian LTS Advisory DLA-2729-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Chris Lamb
August 04, 2021   https://wiki.debian.org/LTS
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Package : asterisk
Version : 1:13.14.1~dfsg-2+deb9u5
CVE ID : CVE-2021-32558
Debian Bug : #991710

It was discovered that there was an issue in the Asterisk telephony
system. If the IAX2 channel driver received a packet that contained
an unsupported media format, a crash could have occured.

For Debian 9 "Stretch", this problem has been fixed in version
1:13.14.1~dfsg-2+deb9u5.

We recommend that you upgrade your asterisk packages.

For the detailed security status of asterisk please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/asterisk

In addition, Asterisk are tracking this issue as "AST-2021-008".

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS