[Solved]:Lab Exercise 4

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1. Overview

As an ethical hacker you are scanning the target network and identify a potentially vulnerable server. You do some research and find a vulnerability and exploit for the target system. You then launch the exploit to gain root level access to the target!

2. Initial Setup

From your Virginia Cyber Range course, select the Cyber Basics environment. Click “start” to start your environment and “join” to get to your Linux desktop.

Task 1: Perform a network scan to identify a potentially vulnerable server

In Lab 2 you used Nmap to scan your network to identify live targets and the ports open on each target. Review your previous results or complete a new network scan to identify a vulnerable target running Microsoft Directory Services also known as SMB or “Samba”.

Question 1: What is your vulnerable target’s IP address? (.5 point)

Question 2: What is the specific version of the Samba service is running on your target? (.5 point)

Task 2: Examine the details of the vulnerability

You have done some research on these open services and versions and it looks like the best vulnerability to use for an exploit is going to be the Samba vulnerability CVE-2017-7494. Learn about this vulnerability at the National Vulnerability Database here:

https://nvd.nist.gov/vuln/detail/CVE-2017-7494

Search the Exploit database https://www.exploit-db.com/ to find a Metasploit module for the identified CVE number.

Question 3: What is the name of the Metasploit Module? (.5 point)

Now that we have identified a vulnerability to exploit and know the Metasploit module name, it is time to get serious.

Task 3: Run Metasploit

Metasploit is a penetration testing framework that comes installed in Kali Linux. Metasploit commands are run from the command line.

First you need to start Metasploit Framework Console (msfconsole). There are several steps to properly starting the msfconsole.

First, you need to start the postgresql database service. This database is used by Metasploit to store information gathered via penetration testing activities. You will have to provide the password (which is student) when running this command.

service postgresql start

Second, you will have to initialize the msf database using the msfdb init command as follows. You will need to use the sudo command to run this command with root level privileges.

sudo msfdb init

Finally, you can start the Metasploit Framework Console by using the msfconsole command as follows:

msfconsole

The msfconsole will start and give you the msf> prompt once the startup has completed. While you are in the msfconsole, regular Linux commands will no longer work.

To see a list of commands that are available from the msf> prompt, type a ? and press enter. (you will need to scroll up to see everything)

The first command you will use is the search command which will allow you to look for information on the Metasploit exploit that you will use for this penetration test.

You can search for a CVE number or a Metasploit module name. Use the search command to look for the Metasploit module that corresponds to the vulnerability you discovered.

The search command shows there is an exploit, the location of the exploit, disclosure date, the rank, and the description of the exploit. You can now use this information to exploit the target.

Question 4: What is the disclosure date and rank of the exploit? (.5 point)

Next you will use the use command to load the exploit. When using the use command, you have to use the full path as shown in the name column of the search results.

The prompt will change to show the name of the exploit that was loaded.
Now use the options command to see the options for the exploit:

options

If you look at the options list, the first option RHOST is blank and is required. RHOST stands for Remote Host and is the IP address of the target system. Whenever you are attempting to exploit a target system, you always have to provide an RHOST. RPORT is also required but it is already set.

You can use the set command to set the RHOST option using the following command. Remember the target_ip is the IP address of the target system identified in Question 1.

set rhost target_ip

Once the RHOST option is set, you can then use the exploit command to launch the exploit.

If the exploit fails the first time, check to make sure the target IP address (RHOST) is correct using the options command and run the exploit again. If the exploit succeeds, you will get Command shell session 1 opened message. This means you have successfully executed the exploit against the target system.

After the Command shell session 1 opened message, you will just have a blinking cursor and no indication that you have entered a shell on the target system. Use the whoami command to see what account you are logged in as in the shell on the target system as follows:

whoami

Question 5: Paste a screenshot that shows your whoami here. (.5 point)

By the answer to whoami, you should know whether the exploit was successful. If so - Congratulations, if everything went well you now pwn the target system! You identified a target, identified a vulnerability in that target, and used Metasploit to exploit the target to get root shell access to the target.

At this point you can run other commands such as pwd, ls, etc. to learn about your exploited target system.

The basic shell is a little difficult to work with as it gives you no prompt and no feedback if the command you execute fails. You can get a more usable shell by using a python script. Use the following command to create a more useful shell on the target system:

python -c 'import pty; pty.spawn("/bin/bash")'

This command uses the python programming language to create a new bash shell. Bash is the default shell used in Linux.

Now that you pwn the system let’s grab a copy of the /etc/shadow file. An attacker would copy this file offline to crack user passwords and try the same passwords on other systems.

Question 6: Paste a screenshot that shows the target’s /etc/shadow file here. (.5 point)

Task 4: Identifying and Correcting Potential Buffer Overflows

Buffer overflow attacks are often a direct result of poor programming practices. Examine the following code and answer the questions below it:

void main()
{
char source[] = “username12”;
char destination[8];
strcpy(destination, source);

return 0;
}

Question 7: Explain why this code has the potential for a buffer overflow. (1 point)

Question 8: Show a way you can fix this code to mitigate the buffer overflow. (1 point)

Examine the following code and answer the questions below it:

#include <stdio.h>
#include <string.h>

int main(void)
{
char buff[15];
int pass = 0;

printf("\n Enter the password : \n");
gets(buff);

if(strcmp(buff, "thegeekstuff"))
{
printf ("\n Wrong Password \n");
}
else
{
printf ("\n Correct Password \n");
pass = 1;
}

if(pass)
{
/* Now Give root or admin rights to user*/
printf ("\n Root privileges given to the user \n");
}

return 0;
}

Question 9: Explain why this code has the potential for a buffer overflow. (1 point)

Question 10: Show a way you can fix this code to mitigate the buffer overflow. (1 point)

By submitting this assignment you are digitally signing the honor code, “I pledge that I have neither given nor received help on this assignment”.

END OF EXERCISE

References

https://metasploit.help.rapid7.com/docs