However, if you run an installation in which not all users are mutually

trusting, or if you maintain an application or extension that is

intended for use in arbitrary situations, it is strongly recommended

that you read the documentation changes described in the first changelog

entry below, and take suitable steps to ensure that your installation or

code is secure.

</para>

<para>

Also, the changes described in the second changelog entry below may

cause functions used in index expressions or materialized views to fail

during auto-analyze, or when reloading from a dump. After upgrading,

monitor the server logs for such problems, and fix affected functions.

</para>

<para>

Also, if you are upgrading from a version earlier than 9.3.18,

<listitem>

<para>

Document how to configure installations and applications to guard

against search-path-dependent trojan-horse attacks from other users

(Noah Misch)

</para>

<para>

Using a <varname>search_path</varname> setting that includes any

schemas writable by a hostile user enables that user to capture

control of queries and then run arbitrary SQL code with the

permissions of the attacked user. While it is possible to write

queries that are proof against such hijacking, it is notationally

tedious, and it's very easy to overlook holes. Therefore, we now

recommend configurations in which no untrusted schemas appear in

one's search path. Relevant documentation appears in

<xref linkend="ddl-schemas-patterns"> (for database administrators and users),

<xref linkend="libpq-connect"> (for application authors),

<xref linkend="extend-extensions-style"> (for extension authors), and

<xref linkend="sql-createfunction"> (for authors

of <literal>SECURITY DEFINER</literal> functions).

(CVE-2018-1058)

</para>

</listitem>

<listitem>

<para>

Avoid use of insecure <varname>search_path</varname> settings

in <application>pg_dump</application> and other client programs

(Noah Misch, Tom Lane)

</para>

<para>

<application>pg_dump</application>,

<application>pg_upgrade</application>,

<application>vacuumdb</application> and

other <productname>PostgreSQL</productname>-provided applications were

themselves vulnerable to the type of hijacking described in the previous

changelog entry; since these applications are commonly run by

superusers, they present particularly attractive targets. To make them

secure whether or not the installation as a whole has been secured,

modify them to include only the <structname>pg_catalog</structname>

schema in their <varname>search_path</varname> settings.

Autovacuum worker processes now do the same, as well.

</para>

<para>

In cases where user-provided functions are indirectly executed by

these programs &mdash; for example, user-provided functions in index

expressions &mdash; the tighter <varname>search_path</varname> may

result in errors, which will need to be corrected by adjusting those

user-provided functions to not assume anything about what search path

they are invoked under. That has always been good practice, but now

it will be necessary for correct behavior.

(CVE-2018-1058)

</para>

</listitem>

However, if you run an installation in which not all users are mutually

trusting, or if you maintain an application or extension that is

intended for use in arbitrary situations, it is strongly recommended

that you read the documentation changes described in the first changelog

entry below, and take suitable steps to ensure that your installation or

code is secure.

</para>

<para>

Also, the changes described in the second changelog entry below may

cause functions used in index expressions or materialized views to fail

during auto-analyze, or when reloading from a dump. After upgrading,

monitor the server logs for such problems, and fix affected functions.

</para>

<para>

Also, if you are upgrading from a version earlier than 9.4.13,

<listitem>

<para>

Document how to configure installations and applications to guard

against search-path-dependent trojan-horse attacks from other users

(Noah Misch)

</para>

<para>

Using a <varname>search_path</varname> setting that includes any

schemas writable by a hostile user enables that user to capture

control of queries and then run arbitrary SQL code with the

permissions of the attacked user. While it is possible to write

queries that are proof against such hijacking, it is notationally

tedious, and it's very easy to overlook holes. Therefore, we now

recommend configurations in which no untrusted schemas appear in

one's search path. Relevant documentation appears in

<xref linkend="ddl-schemas-patterns"> (for database administrators and users),

<xref linkend="libpq-connect"> (for application authors),

<xref linkend="extend-extensions-style"> (for extension authors), and

<xref linkend="sql-createfunction"> (for authors

of <literal>SECURITY DEFINER</literal> functions).

(CVE-2018-1058)

</para>

</listitem>

<listitem>

<para>

Avoid use of insecure <varname>search_path</varname> settings

in <application>pg_dump</application> and other client programs

(Noah Misch, Tom Lane)

</para>

<para>

<application>pg_dump</application>,

<application>pg_upgrade</application>,

<application>vacuumdb</application> and

other <productname>PostgreSQL</productname>-provided applications were

themselves vulnerable to the type of hijacking described in the previous

changelog entry; since these applications are commonly run by

superusers, they present particularly attractive targets. To make them

secure whether or not the installation as a whole has been secured,

modify them to include only the <structname>pg_catalog</structname>

schema in their <varname>search_path</varname> settings.

Autovacuum worker processes now do the same, as well.

</para>

<para>

In cases where user-provided functions are indirectly executed by

these programs &mdash; for example, user-provided functions in index

expressions &mdash; the tighter <varname>search_path</varname> may

result in errors, which will need to be corrected by adjusting those

user-provided functions to not assume anything about what search path

they are invoked under. That has always been good practice, but now

it will be necessary for correct behavior.

(CVE-2018-1058)

</para>

</listitem>