Tag: PostgreSQL (Page 1 of 2)

The flashmq.com project has afforded me an opportunity to finally play with PostgREST—a technology that, for many years, I had been itching to use, even before I ever heard of PostgREST; the itch started back in the day when Wiebe and I were working with Ruby on Rails and I tried to hack ActiveRecord to propagate PostgreSQL its permissions into the controller layer, wishing to leave permission checking to the RDBMS rather than redoing everything in the controller.

One habit that changed between 2007 (when I was still working with ActiveRecord) and now (with my most recent torture being by Django’s horrid ORM) is that I no longer rely on PostgreSQL its search_path for anything. Instead, I tend to use qualified names for pretty much anything. But, because one should never stop doubting ones own choices, recently I did some digging and testing to see if there really are no valid, safe use cases for the use of unqualified names in PostgreSQL…

Before delving into the use cases, I want to ruminate on the definitional knowledge: firstly, about Postgres schemas in general, and secondly, about the search_path.

PostgreSQL schemas

• PostgreSQL enables the division of a database into namespaces called schemas.
• Schemas can contain tables, views, types, domains, functions, procedures, and operators.
• Schemas are flat, in that they cannot contain other schemas.
• Schemas are a part of the SQL standard, and, as such, other big name RDBMSs support schemas too, except, naturally, my least favorite of them all—the database I love to hate—MySQL.
• An object (such as a table) its fully qualified name consists of the schema name, followed by a dot, followed by its local name. For example: pg_catalog.pg_cast. (Incidentally, casts are one of the few types of entities that are not schema-bound.)
• Fresh PostgreSQL databases contain a public schema by default.
  • This standard public schema is part of the (modifiable) template1 database that is copied when you CREATE DATABASE (without TEMPLATE = template parameter).
  • Prior to PostgreSQL 15, the template1 database was set up such that PUBLIC (as in everyone—all roles) had CREATE permissions in the public schema.
    • This was bad, mkay? The reason being CVE-2018-1058: the public schema is in the default search_path (see below), and routines in public could be created with higher specificity (and thus precedence over) their identically-named counterparts in the system-standard pg_catalog schema.
    • If, for some reason, you are using Postgres its public schema, you should more likely than not REVOKE CREATE ON SCHEMA public FROM PUBLIC.
• Objects can also be identified by just their schema-local name, thanks to the search_path—a list of PostgreSQL schemas which are searched for the object name. For instance, you will see references to the now() function rather than pg_catalog.now().

PostgreSQL its effective search path and how it’s derived from the search_path setting

• When using an unqualified object name, the schemas in the effective search path are searched, first to last.
  • The object that is selected from the searched schemas is, among those with the highest specificity, the one that is found earliest in the effective search path.
    • Specificity matters, for routines and operators: a function with a better-matching type signature that is found later in the effective search path will be chosen over a more generic match that is found earlier.
• The schemas in the effective search path can be retrieved from the current_schemas(false) function.

  SET search_path TO DEFAULT;
  SELECT current_setting('search_path'),
         current_schemas(false);

  This will give us the search_path setting side-by-side with the effective search path that is derived from it:

  SET
   current_setting | current_schemas
  -----------------+-----------
   "$user", public | {public}

  • With current_schemas(true), the implicitly-searched schemas are also included in the returned name[] array.

    SET search_path TO DEFAULT;
    
    CREATE TEMPORARY TABLE a (id INT);
    
    SELECT current_setting('search_path'),
           current_schemas(true);
    

    SET
    CREATE TABLE
     current_setting |        current_schemas
    -----------------+-------------------------------
     "$user", public | {pg_temp_3,pg_catalog,public}
    (1 row)
    

• The effective search path is derived from the search_path setting:
  • Schemas that don’t exist or are inaccessible to the current_user are subtracted from the search_path.

    CREATE SCHEMA need_to_know_basis;
    CREATE ROLE no_need_to_know;
    
    GRANT USAGE
      ON SCHEMA public
      TO no_need_to_know;
    
    SET ROLE TO no_need_to_know;
    
    SET search_path TO need_to_know_basis, "$user", public;
    
    SELECT current_setting('search_path'),
           current_schemas(false);
    

    CREATE SCHEMA
    CREATE ROLE
    GRANT
    SET
    SET
               current_setting           | current_schemas
    -------------------------------------+-----------------
     need_to_know_basis, "$user", public | {public}
    (1 row)
    

  • "$user" is expanded into current_user if a schema by that name exists and is accessible to the current user:

    DROP ROLE IF EXISTS bondjames;
    DROP SCHEMA IF EXISTS bondjames;
    
    CREATE ROLE bondjames;
    CREATE SCHEMA AUTHORIZATION bondjames;
    
    SET ROLE TO bondjames;
    
    SET search_path TO DEFAULT;
    
    SELECT current_setting('search_path'),
           current_schemas(false);
    

    CREATE ROLE
    CREATE SCHEMA
    SET
    SET
     current_setting | current_schemas
    -----------------+-----------------
     "$user", public | {bondjames}
    (1 row)
    

  • pg_catalog is always included in the effective search path.
    • If pg_catalog is not explicitly included in the search_path, it is implicitly prepended to the very beginning of the search_path:

      SET search_path TO DEFAULT;
      
      SELECT current_setting('search_path'),
             current_schemas(true);
      

      SET
       current_setting |   current_schemas
      -----------------+---------------------
       "$user", public | {pg_catalog,public}
      (1 row)
      

  • pg_temp is also included in the effective search path, if it exists—that is, if any temporary objects have been created.
    • When pg_temp exists is omitted from the explicit search_path setting, it is prepended implicitly in front of the search_path, even before pg_catalog.
    • pg_temp is expanded into the actual pg_temp_nnn for the current session.
    • “[T]he temporary schema is only searched for relation (table, view, sequence, etc.) and data type names. It is never searched for function or operator names.”
      • This default behavior—to never search pg_temp for function names and operators—was introduced in 2007 in response to CVE-2007-2138. From the release notes:

        “This [was] needed to allow a security-definer function to set a truly secure value of search_path. Without it, an unprivileged SQL user can use temporary objects to execute code with the privileges of the security-definer function (CVE-2007-2138). See CREATE FUNCTION for more information.”

• The default Postgres search_path is:

  SET search_path TO DEFAULT;
  
  SELECT current_setting('search_path');
  SHOW search_path;

  SET
   current_setting
  -----------------
   "$user", public
  (1 row)
  
     search_path
  -----------------
   "$user", public
  (1 row)
  

Routine-specific search_path settings

Like many settings in PostgreSQL, search_path can be set on many levels:

1. In the postgresql.conf config file:

   search_path = '"$user", public'

2. At the user/role level:

   ALTER ROLE { role_specification | ALL } [ IN DATABASE database_name ] SET search_path { TO | = } { value | DEFAULT }
   ALTER ROLE { role_specification | ALL } [ IN DATABASE database_name ] SET search_path FROM CURRENT
   ALTER ROLE { role_specification | ALL } [ IN DATABASE database_name ] RESET search_path

3. At the database level:

   ALTER DATABASE name SET search_path { TO | = } { value | DEFAULT };
   ALTER DATABASE name SET search_path FROM CURRENT;
   ALTER DATABASE name RESET search_path;

4. And at the routine level:

   ALTER FUNCTION name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       SET search_path { TO | = } { value | DEFAULT };
   ALTER FUNCTION name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       SET search_path FROM CURRENT;
   ALTER FUNCTION name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       RESET search_path;
   ALTER PROCEDURE name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       SET search_path { TO | = } { value | DEFAULT };
   ALTER PROCEDURE name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       SET search_path FROM CURRENT;
   ALTER PROCEDURE name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ]
       RESET search_path;
   

Importantly, all these settings set defaults. They do not stop the user (or a VOLATILE function/procedure) from overriding that default by issuing:

SET search_path TO evil_schema, pg_catalog;

Or, if the user doesn’t have their own evil_schema:

select set_config('search_path', 'pg_temp, pg_catalog');

In the following example, SUPERUSER wortel innocuously uses lower() in a SECURITY DEFINER function, naively assuming that it’s implicitly referring to pg_catalog.lower():

CREATE ROLE wortel WITH SUPERUSER;

SET ROLE wortel;

CREATE SCHEMA myauth;
GRANT USAGE
  ON SCHEMA myauth
  TO PUBLIC;

CREATE FUNCTION myauth.validate_credentials(email$ text, password$ text)
  RETURNS BOOLEAN
  SECURITY DEFINER
  LANGUAGE PLPGSQL
  AS $$
DECLARE
  normalized_email text;
BEGIN
  normalized_email := lower(email$);

  -- Something interesting happens here…

  RETURN TRUE;
END;
$$;
GRANT EXECUTE
  ON FUNCTION myauth.validate_credentials
  TO PUBLIC;

wortel creates a new user piet and gives piet his own schema, assuming that he can only do damage to his own little garden:

CREATE ROLE piet;
CREATE SCHEMA AUTHORIZATION piet;

However, piet turns out to be wearing his black hat today:

SET ROLE piet;

SET search_path TO DEFAULT;
SELECT current_setting('search_path'), current_schemas(true);

SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

CREATE FUNCTION piet.lower(text)
  RETURNS TEXT
  LANGUAGE plpgsql
  AS $$
BEGIN
  RAISE NOTICE 'I can now do nasty stuff as %!', current_user;
  RETURN pg_catalog.lower($1);
END;
$$;

SET search_path TO piet, pg_catalog;  -- Reverse order;
SELECT current_setting('search_path'), current_schemas(true);

SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

SET
SET
 current_setting |  current_schemas
-----------------+-------------------
 "$user", public | {pg_catalog,piet}
(1 row)

 validate_credentials
----------------------
 t
(1 row)

CREATE FUNCTION
SET
 current_setting  |  current_schemas
------------------+-------------------
 piet, pg_catalog | {piet,pg_catalog}
(1 row)

NOTICE:  I can now do nasty stuff as superuser!
 validate_credentials
----------------------
 t
(1 row)

This can be mitigated by attaching a specific search_path to the SECURITY DEFINER routine:

RESET ROLE;

ALTER FUNCTION myauth.validate_credentials
  SET search_path = pg_catalog;

SET ROLE piet;
SET search_path TO piet, pg_catalog;  -- Reverse order;
SELECT current_setting('search_path'), current_schemas(true);
SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

RESET
ALTER FUNCTION
SET
SET
 current_setting  |  current_schemas
------------------+-------------------
 piet, pg_catalog | {piet,pg_catalog}
(1 row)

 validate_credentials
----------------------
 t
(1 row)

Before the changes made in response to CVE-2007-2138, piet would have been able to mask pg_catalog.lower with his own pg_temp.lower() even if he did not muck around with the search_path. After all, by default, pg_temp is prepended to the very front of the effective search path:

CREATE ROLE wortel WITH SUPERUSER;

SET ROLE wortel;

CREATE SCHEMA myauth;
GRANT USAGE
  ON SCHEMA myauth
  TO PUBLIC;

CREATE FUNCTION myauth.validate_credentials(email$ text, password$ text)
  RETURNS BOOLEAN
  SECURITY DEFINER
  LANGUAGE PLPGSQL
  AS $$
DECLARE
  normalized_email text;
BEGIN
  normalized_email := lower(email$);

  -- Something interesting happens here…

  RAISE NOTICE 'My effective search path is: %', current_schemas(true);

  RETURN true;
END;
$$;
GRANT EXECUTE
  ON FUNCTION myauth.validate_credentials
  TO PUBLIC;

DROP SCHEMA piet CASCADE;
DROP ROLE piet;
CREATE ROLE piet;

SET ROLE piet;

SET search_path TO DEFAULT;
SELECT current_setting('search_path'), current_schemas(true);

SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

CREATE FUNCTION pg_temp.lower(text)
  RETURNS TEXT
  LANGUAGE plpgsql
  AS $$
BEGIN
  RAISE NOTICE 'I can now do nasty stuff as %!', current_user;
  RETURN pg_catalog.lower($1);
END;
$$;

SELECT current_setting('search_path'), current_schemas(true);

SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

RESET ROLE;

ALTER FUNCTION myauth.validate_credentials
  SET search_path = pg_catalog;

SET ROLE piet;
SELECT current_setting('search_path'), current_schemas(true);
SELECT myauth.validate_credentials('pietje@example.com', 'Piet zijn password');

CREATE ROLE
SET
CREATE SCHEMA
GRANT
CREATE FUNCTION
GRANT
ERROR:  schema "piet" does not exist
DROP ROLE
CREATE ROLE
SET
SET
 current_setting | current_schemas
-----------------+-----------------
 "$user", public | {pg_catalog}
(1 row)

NOTICE:  My effective search path is: {pg_catalog,public}
 validate_credentials
----------------------
 t
(1 row)

CREATE FUNCTION
 current_setting |    current_schemas
-----------------+------------------------
 "$user", public | {pg_temp_3,pg_catalog}
(1 row)

NOTICE:  My effective search path is: {pg_temp_3,pg_catalog,public}
 validate_credentials
----------------------
 t
(1 row)

RESET
ALTER FUNCTION
SET
 current_setting |    current_schemas
-----------------+------------------------
 "$user", public | {pg_temp_3,pg_catalog}
(1 row)

NOTICE:  My effective search path is: {pg_temp_3,pg_catalog}
 validate_credentials
----------------------
 t
(1 row)

As you can see, now this approach doesn’t work anymore, even though the effective search path includes pg_temp_3 (logically so because it is omitted in the search_path that is SET on the routine level). That is because part of the fix for CVE-2007-2138 was that unqualified routine and function names are never searched for in the temporary schema name. (The other part of the fix was that pg_temp can be listed explicitly in the search_path to also give it lower precedence for relation names.)

Before PostgreSQL 15, there was another way in which piet would have been able to mask pg_catalog.lower(): by creating the function in public, which was, until Pg 15, fair game for all roles to CREATE FUNCTIONs in.

Pro tip: you can use CREATE { FUNCTION | ROUTINE } … SET search_path FROM CURRENT to take the search_path from the migration context.

When unqualified names in table column default value expressions are evaluated

So, now we know how to control the search_path of tables so that we don’t have to write out every operator within each function in a form like:

SELECT 3 OPERATOR(pg_catalog.+) 4;

How about the DEFAULT expressions for columns in table definitions? And, similarly, what about GENERATED ALWAYS AS expressions?

If a table is wrapped inside a view for security, can evil_user mask, for instance, the now() function with evil_user.now() and have evil_user.now() be executed as the view’s definer?

No:

“Functions called in the view are treated the same as if they had been called directly from the query using the view. Therefore, the user of a view must have permissions to call all functions used by the view. Functions in the view are executed with the privileges of the user executing the query or the function owner, depending on whether the functions are defined as SECURITY INVOKER or SECURITY DEFINER. Thus, for example, calling CURRENT_USER directly in a view will always return the invoking user, not the view owner. This is not affected by the view’s security_invoker setting, and so a view with security_invoker set to false is not equivalent to a SECURITY DEFINER function and those concepts should not be confused.”

But is the same true for when the table is wrapped by one of these MS Certified Suit-style wrapper functions? This would depend on when the unqualified object names are resolved into schema-qualified names—during table definition or during INSERT or UPDATE. So when does this happen? Well, that is a bit difficult to spot:

BEGIN TRANSACTION;

CREATE ROLE wortel WITH SUPERUSER;
SET ROLE wortel;

CREATE SCHEMA protected;

CREATE SEQUENCE protected.thingy_id_seq;
CREATE TABLE protected.thingy (
  id BIGINT
    PRIMARY KEY
    DEFAULT nextval('protected.thingy_id_seq')
  ,id2 UUID
    UNIQUE
    DEFAULT gen_random_uuid()
  ,inserted_by_application NAME
    DEFAULT current_setting('application_name')
  ,inserted_at TIMESTAMPTZ
    DEFAULT now()
  ,description TEXT
);

SELECT pg_get_expr(adbin, 'protected.thingy'::regclass::oid)
FROM   pg_catalog.pg_attrdef
WHERE  adrelid = 'protected.thingy'::regclass::oid;

CREATE SCHEMA exposed;

CREATE FUNCTION exposed.insert_thingy(TEXT)
  RETURNS BIGINT
  SECURITY DEFINER
  LANGUAGE PLPGSQL
  AS $$
DECLARE
  _new_id BIGINT;
BEGIN
  RAISE NOTICE 'current_schemas(true) = %', current_schemas(true);

  INSERT INTO protected.thingy (description)
    VALUES ($1)
    RETURNING id
    INTO _new_id;
  RETURN _new_id;
END;
$$;

CREATE ROLE evil_user;
CREATE SCHEMA AUTHORIZATION evil_user;

GRANT USAGE
  ON SCHEMA exposed
  TO evil_user;
GRANT EXECUTE
  ON FUNCTION exposed.insert_thingy
  TO evil_user;

SET ROLE evil_user;

CREATE FUNCTION evil_user.nextval(regclass)
  RETURNS BIGINT
  LANGUAGE PLPGSQL
  AS $$
BEGIN
  RAISE NOTICE 'I am now running as: %', current_user;

  RETURN 666;
END;
$$;

CREATE FUNCTION evil_user.now()
  RETURNS TIMESTAMPTZ
  LANGUAGE PLPGSQL
  AS $$
BEGIN
  RAISE NOTICE 'I am now running as: %', current_user;

  RETURN pg_catalog.now();
END;
$$;

SET search_path TO evil_user, pg_catalog;  -- Reverse path

SELECT exposed.insert_thingy('This is a thing');

RESET ROLE;

SHOW search_path;

SELECT pg_get_expr(adbin, 'protected.thingy'::regclass::oid)
FROM   pg_catalog.pg_attrdef
WHERE  adrelid = 'protected.thingy'::regclass::oid;

BEGIN
CREATE ROLE
SET
CREATE SCHEMA
CREATE SEQUENCE
CREATE TABLE
                 pg_get_expr
----------------------------------------------
 nextval('protected.thingy_id_seq'::regclass)
 gen_random_uuid()
 current_setting('application_name'::text)
 now()
(4 rows)

CREATE SCHEMA
CREATE FUNCTION
CREATE ROLE
CREATE SCHEMA
GRANT
GRANT
SET
CREATE FUNCTION
CREATE FUNCTION
SET
NOTICE:  current_schemas(true) = {evil_user,pg_catalog}
 insert_thingy
---------------
             1
(1 row)

RESET
      search_path
-----------------------
 evil_user, pg_catalog
(1 row)

                       pg_get_expr
---------------------------------------------------------
 pg_catalog.nextval('protected.thingy_id_seq'::regclass)
 gen_random_uuid()
 current_setting('application_name'::text)
 pg_catalog.now()
(4 rows)

As you can see, pg_get_expr() has only disambiguated the functions that evil_user has tried to mask. Conclusion: yes, schema-binding happens when the DDL (CREATE or ALTER TABLE) is executed.

No need to worry about security holes here, as long as you are aware of the search_path with which you are running your migrations. (You are using some sort of migration script, are you not? The only valid answer in the negative is if instead you’re managing your PostgreSQL schemas via extension upgrade scripts.)

Valid and less valid search_path use cases

Despite the deep-dive in all the caveats above, the search_path is not all bad. We can now be very precise about the context in which it’s reasonably safe to rely on the search_path:

• within SECURITY INVOKER routines, because these are executed with the privileges of the caller (but see below for further caveats);
• within SECURITY DEFINER routines for which SET search_path is explicitly specified;
• within CREATE TABLE and CREATE VIEW DDL statements, as long as you are aware of the search_path at the time of creation, as the schema-binding will happen during creation.

Do note that even without escalated privileges, the unsuspected masking of a function by a malicious function could still result in, for instance, prices for a certain user always amounting to zero, or the random password reset string being not so random. Therefore, here are some context in which you should never rely on the search_path:

• when there are schemas in the search_path which you do not trust 100%;
• within SECURITY DEFINER routines for which SET search_path is not explicitly specified;
• (trigger) routines that are supposed to produce something random (unless if these are protected by SET search_path;

That all sounds terribly complicated. That begs the question: are there, in fact, use cases which would justify us to not just blanket schema-qualify ever-y-thing?

Use case: brevity

If you consider that operators are schema-qualified objects too, you will most likely want to at least allow yourself and your team to forego the typing of 3 + 4 instead of 3 OPERATOR(pg_catalog.+) 4 in the body of your routines. Admittedly, this is not a very strong argument in favor of the search_path, but there is no harm in it as long as your define your routines with SET search_path.

Use case: polymorphism

When I define a poymorphic routine with anyelement, anyarray or anyanything pseudo-types in its signature, I want the routine to be able to apply functions and operators to its arguments regardless of whether these (overloaded) functions and operators already existed in a schema that I was aware of at the time of CREATE-ing the routine.

Suppose I have a polymorphic function called sum_price_lines(anyarray):

BEGIN TRANSACTION;

CREATE FUNCTION pricing.sum_price_lines(anyarray)
  RETURNS anyelement
  LANGUAGE plpgsql
  AS $$
BEGIN
  RETURN (
    SELECT
      SUM(net_price(line))
    FROM
      unnest($1) AS line
  );
END;
$$;

CREATE FUNCTION pricing.net_price(int)
  RETURNS int
  LANGUAGE SQL
  RETURN $1;

SET search_path TO pricing;

SELECT pricing.sum_price_lines('{1,2,3,4}'::int[])

sum_price_lines() calls net_price on each individual member of its anyarray argument. With the supplied function, this doesn’t do anything useful, but the creator of the invoicing schema can for instance use this to sum rows of the invoicing.invoice_line table type, simply by creating an overloaded invoicing.net_price(invoicing.invoice_line[]) function and making sure that it can be found in the search_path.

Use case: function and operator overloading

And indeed overloading (also of operators) is a very important use case of the search_path. Being able to define +, -, and * for anything, from order lines, to invoice lines, to quotation lines, and to users even is a valuable tool, that we wouldn’t want to be taken away from us entirely by a lacking understanding of search_path security.

Use case: overriding/masking objects in another schema

I got re-interested in relying on the search_path rather than on schema-qualified names while I was working on an extension to make mocking the pg_catalog.now() function (or other functions) easy and performant. Because table defaults are schema-bound during CREATE TABLE time, I couldn’t rely on the search_path to mask pg_catalog.now() with mockable.now(). Instead, I use mockable.now() directly, which, when the mocker is not active, is just a thin wrapper around pg_catalog.now(), which the query planner should be able to inline completely without trouble.

But there are other use cases in which schema masking can be very useful. For instance, if you want to offer a specific extension schema to your … extension. Maybe you want to offer a table with factory defaults and rather than have the user TRUNCATE the table (and make upgrades and comparisons to the factory-default data a headache), you allow them (or some function/producedure, possible triggered from a view) to create a table of their own. Let me know if you know or can come up with more good examples.

Some words of thanks

Thanks to the Postgres ecosystem

I wish to express my gratitude towards the ever-solid developers of PostgreSQL, who have kept improving PostgreSQL at a steady, sustainable pace in the 15 years since I last seriously used it in 2007. All the features that I wished were there in 2007 have since been implemented, including, very recently, in PostgreSQL, WITH (security_invoker) for views. A guilty pleasure from my last long-term stint at a wage slave working with Django’s ORM was to every now and then glare at the PostgreSQL feature matrix and fantasize about being able to really unleash this beast without being hindered by the lowest common denominator (MySQL) that ORMs tend to cater to.

And thanks to the excellent PostgREST, I can now do what I dreamt of for years. And yes, for years, I’ve dreamt precisely of using PostgREST rather than all the ridiculously inefficient, verbose, and mismatched layers around SQL that things like the django-rest-framework forced upon me. Indeed, as François-Guillaume Ribreau testified, “it feels like cheating!”

Thanks to friends

The motivation for deep-diving into PostgreSQL again, after quite a few years wherein the power of PostgreSQL was buffered by Django in my day job, came from an excellent MQTT broker written by my buddy Wiebe. Me and another friend—Jeroen—where so impressed by the speed and robustness of this MQTT server software that we decided to build a managed MQTT hosting business around it. And we’ve been building all this goodness around the FlashMQ FOSS core with a very solid PostgreSQL core, a PostgREST API and a Vue.JS/Nuxt front + back-end. Some daemons hover around the PostgreSQL core and connect directly to it (through dedicated schemas, to confirm to my Application-Exclusive Schema Scoping (AESS) practice), so that it all resembles a very light-weight micro-services architecture.

Further reading

• The Schemas section in the Data Definition chapter.
• The search_path setting in the Client Connection Defaults documentation
• The Writing SECURITY DEFINER Functions Safely section in the CREATE FUNCTION documentation.
• The Session Information Functions table in the System Information Functions and Operators section documents
  • the current_schema() function
    • (and its current_schema alias),
  • as well as current_schemas().
• CVE-2007-2138 resulted in 2 changes:
  1. “Support explicit placement of the temporary-table schema within search_path”
  2. “and disable searching it for functions and operators (Tom)”.
• CVE-2018-1058 initially resulted only in additional documentation to explain user how to avoid this type of attack: A Guide to CVE-2018-1058: Protect Your Search Path
  • Years later, in PostgreSQL 15, the vanilla template1 database was changed to no longer GRANT CREATE ON SCHEMA public TO PUBLIC.