PostGIS 2.x before 2.3.3, as used with PostgreSQL, allows remote attackers to cause a denial of service via crafted ST_AsX3D function input, as demonstrated by an abnormal server termination for "SELECT ST_AsX3D('LINESTRING EMPTY');" because empty geometries are mishandled.
https://trac.osgeo.org/postgis/changeset/15445
https://trac.osgeo.org/postgis/changeset/15444
https://lists.debian.org/debian-lts-announce/2021/12/msg00020.html
https://lists.debian.org/debian-lts-announce/2019/01/msg00030.html