A PostgreSQL security update has been released for Ubuntu Linux 16.04 LTS.

[USN-6366-1] PostgreSQL vulnerability

==========================================================================
Ubuntu Security Notice USN-6366-1
September 13, 2023

postgresql-9.5 vulnerability
==========================================================================

A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 16.04 LTS (Available with Ubuntu Pro)

Summary:

PostgreSQL could be made to execute commands as the bootstrap superuser.

Software Description:
- postgresql-9.5: Object-relational SQL database

Details:

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.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
  postgresql-9.5                     9.5.25-0ubuntu0.16.04.1+esm5
  postgresql-client-9.5           9.5.25-0ubuntu0.16.04.1+esm5

After a standard system update you need to restart PostgreSQL to make
all the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-6366-1
  CVE-2023-39417