A postgis security update has been released for Debian GNU/Linux 9 LTS to address a denial of service issue.

DLA 2857-1: postgis security update

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Debian LTS Advisory DLA-2857-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Adrian Bunk
December 28, 2021   https://wiki.debian.org/LTS
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Package : postgis
Version : 2.3.1+dfsg-2+deb9u1
CVE ID : CVE-2017-18359

In PostGIS, which adds support for geographic objects to the PostgreSQL
database, denial of service via crafted ST_AsX3D function input was
fixed.

For Debian 9 stretch, this problem has been fixed in version
2.3.1+dfsg-2+deb9u1.

We recommend that you upgrade your postgis packages.

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

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