postgresql-12, postgresql-14, postgresql-15 vulnerabilities

It was discovered that PostgreSQL incorrectly handled certain extension
script substitutions. An attacker having database-level CREATE privileges
can use this issue to execute arbitrary code as the bootstrap superuser.
(CVE-2023-39417)

It was discovered that PostgreSQL incorrectly handled the MERGE command. A
remote attacker could possibly use this issue to bypass certain UPDATE and
SELECT policies. This issue only affected Ubuntu 23.04. (CVE-2023-39418)