Nahamcon2021 CTF - Internal - Writeup

Introduction

Today we're doing a CTF writeup for the Internal challenge from the NahamCon2021 CTF. Internal is a Linux PrivEsc challenge, and after we start the challenge we received a string we can use to interact with the challenge:


The first thing we do is log in to the system as the orion user using captured SSH credentials we obtained from a a previous challenge:

ssh -p 30718 orion@challenge.nahamcon.com
input password: stars4love4life


While enumerating running processes, we find some interesting stuff:

ps -aux


The root user is running MySQL as well as a Bash script that references MySQL. Let's take a look at that Bash script:

cat /create_mysql_admin_user.sh


The information in the script indicates that the root account in MySQL is setup without a password. Let's login to MySQL as root now:

mysql -uroot -p
input a blank password


Using MySQL as the root user, we can read any files in the system that we are aware of. Because the common location of the flag.txt file in CTF games is the /root directory, we can use the following SQL command to read it:

SELECT LOAD_FILE('/root/flag.txt');


Summary

After logging into the system, we found indications that the MySQL root account as setup without a password. We were able to authenticate into the MySQL service as the root user, and used MySQL to read the objective flag file.

Finish









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