Escalate_Linux: Vulnhub Walkthrough (Part 1)

Escalate_Linux is an intentionally developed Linux vulnerable virtual machine. The main focus of this machine is to learn Linux Post Exploitation (Privilege Escalation) Techniques. The credit for making this VM machine goes to “Manish Gupta” and it is a boot2root challenge where the creator of this machine wants us to root the machine through twelve different ways. You can download the machine following this link: https://www.vulnhub.com/entry/escalate_linux-1,323/

NOTE: In this article, we have exploited the machine with six different methods.

Security Level: Beginner-Intermediate

Penetrating Methodology:

Scanning

  • Netdiscover
  • Nmap

Enumeration

  • Web Directory Search 

Exploiting

  • Metasploit shell upload
  • LinEnum.sh

Privilege Escalation

  • Method 1: Get root shell by exploiting suid rights of the shell file
  • Method 2: Get a root shell by cracking the root password
  • Method 3: Get root shell by exploiting sudo rights of user1
  • Method 4: Get root shell by exploiting crontab
  • Method 5: Exploiting Sudo rights of vi editor
  • Method 6: Exploiting writable permission of /etc/passwd file

Walkthrough:

Scanning:

Let’s start off by scanning the network using Netdiscover tool and identify the host IP address. We can identify our host IP address as 192.168.0.17.

Now let’s scan the services and ports of target machine with nmap

Enumeration:

As we can see port 80 is open, so we tried to open the IP address in our browser and got nothing but the default Apache webpage.

So we used dirb with .php filter for directory enumeration.

After brute-forcing with dirb, we found a URL named http://192.168.0.17/shell.php

Now we opened the URL in our browser and found that it accepts cmd as get parameter.

So, we passed the id command in the URL and found the results are reflected in the response.

Exploiting

Since the target machine is vulnerable to command injection, we created a web delivery shell using Metasploit.

The target host was not able to run the script directly, so we used URL encoding.

After encoding the script, we were successfully able to run it on the target machine and get the meterpreter session.

We got the bash shell of User6 after using python one-liner shell command.

To further enumerate the target host, we uploaded LinEnum tool on the target host.

From the results of LinEnum scan, we found that the target host has eight users namely user1, user2 up to user8.

We also found that in crontab, a file named autoscript.sh is being run every 5 minutes with root privileges.

From the same LinEnum scan, we came to know that /etc/passwd is writable for users also. Also, we found that we can run shell and script files with root privileges because SUID bit is enabled on it.

Privilege Escalation:

As mentioned above there are multiple ways to do the privilege escalation of this machine.

We will try to do as many methods as possible.

Method 1: Get root shell by exploiting SUID rights of the shell file

Using the find command we can confirm that the shell file located in the home directory of user3 can be executed with root privileges.

We tried to execute the same file and got the root shell.

Method 2: Get a root shell by cracking the root password

From the above screenshot, we know that the script file located in the user5 home directory can be executed with root privileges. Using the Path variable exploitation methodology we can access the /etc/shadow file.

To know more about path variable privilege escalation use this link: https://www.hackingarticles.in/linux-privilege-escalation-using-path-variable/

on executing ./script, we have fetched the content of shadow’s file as shown in the below image.

We copied the hashed password of root user in the hash file and used John The Ripper tool to crack the password. We got the password of the root as 12345 and then using the su command we were able to access as root.

Method 3: Get root shell by exploiting SUDO rights of user1

We already know by now that script file can be executed with root privileges.

Using the same script file we can change the password of all the users with the help of Path variable methodology.

Here we used echo and chpasswd command to replace the existing password with our new password 12345. And then switched to the user1 account using su command. After checking the sudoer’s list for user1 we came to know that this user can run all commands as sudo.

So we ran the command sudo su and got the root access.

Method 4: Get root shell by exploiting crontab

In the previous screenshot, we saw there is a task scheduled after every 5 minutes for user4 in the crontab by the name autoscript.sh. We changed the password of user4 the same way as we did for user1 and then switched to user4 with the new password 12345. There we can see a file autoscript.sh in the Desktop folder.

So what we did is we created a payload using msfvenom and then copied the code into autoscript.sh file using echo.

After copying the code into autoscript.sh file we executed the file and started the netcat listener on our kali machine and waited for the shell.

Yes we got the root shell as the autoscript.sh is executing as root in the crontab.

Method 5: Exploiting SUDO rights of vi editor

We changed the password of all the users to 12345 using the same methodology as above and switched between users to check for more exploits. We found that user8 has a sudo permission for vi editors.

Open the vi editor with sudo and insert sh command as shown in the screenshot below, exit the editor and hurray we got the root shell.

And again we will obtain the root shell as shown below in the image.

Method 6: Exploiting writable permission of /etc/passwd file

Continuing with the enumeration of users, we found that user7 is a member of the root group with gid 0.

And we already know from the LinEnum scan that /etc/passwd file is writable for the user. So from this observation, we concluded that user7 can edit the /etc/passwd file.

So we copied the contents of /etc/passwd file in our kali machine and created a new user named raj with root privileges for which we generated a password pass123 using openssl.

As you can observe we have created a new entry inside /etc/passwd for user raj with root privilege.

On the target machine, we downloaded the edited passwd file in the /etc folder using wget command.

Then we tried to switch to our newly created user raj and YES yet again we proudly got the root shell of the machine.

Conclusion: So in this part-1 of Escalate_Linux we did the privilege escalation by six different methodologies. In the part-2 we will try to exploit the machine by some different methods. So keep visiting Hacking Articles for next part.

Author: Auqib Wani is a Certified Ethical Hacker, Penetration Tester and a Tech Enthusiast with more than 5 years of experience in the field of Network & Cyber Security. Contact Here

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