A coturn security update has been released for Debian GNU/Linux 9 LTS to address a flaw where a remote attacker can bypass the protection via a specially crafted request using a peer address of '0.0.0.0' and trick coturn in relaying to the loopback interface.

DLA 2522-1: coturn security update

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Debian LTS Advisory DLA-2522-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Emilio Pozuelo Monfort
January 12, 2021   https://wiki.debian.org/LTS
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Package : coturn
Version : 4.5.0.5-1+deb9u3
CVE ID : CVE-2020-26262

A flaw was discovered in coturn, a TURN and STUN server for VoIP. By
default coturn does not allow peers on the loopback addresses
(127.x.x.x and ::1). A remote attacker can bypass the protection via a
specially crafted request using a peer address of '0.0.0.0' and trick
coturn in relaying to the loopback interface. If listening on IPv6 the
loopback interface can also be reached by using either [::1] or [::] as
the address.

For Debian 9 stretch, this problem has been fixed in version
4.5.0.5-1+deb9u3.

We recommend that you upgrade your coturn packages.

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

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