- Personal website of Thomas Sluyter

Unimportant background
  RSS feed

About me

Blog archives















> Weblog

> Sysadmin articles

> Maths teaching

Speedrunning Redhat's EX413 exam

2017-09-21 15:16:00

booking confirmation

Over the past few weeks, I've been setting up a pen-testing coaching track for ITGilde. I'd planned my agenda for Q3/Q4/Q1 accordingly and had even accepted that my RHCSA and RHCE certifications would lapse in November. Unfortunately I couldn't get enough students together for this winter, so I'm putting the coaching track off until next spring. Huzzah, this frees up plenty of time for studying!

So... Now I'd like to try and retain my Redhat certs, for which I've worked so hard! My deadline's pretty close though, as November's right around the corner. After some investigation I concluded that the most productive way for me to retain these certs, would be through passing one of the RHCA exams. EX413, pertaining to server security, is right up my alley! So, I'll be speedrunning the EX413 studies, trying to finish it all in five weeks time!

I love a good challenge! ^_^ tags: , ,

View or add comments (curr. 2)

Building an on-premise Stratum-1 NTP server

2017-08-11 13:59:00

Recently I've been poking around NTP time servers with a few friends. Our goal was to create an autonomous, reliable and cheap NTP box that could act as an on-premise, in-house Stratum-1 time server. In a world filled with virtual machines that don't have their own hardware clocks, but whose applications demand very strict timekeeping, this can be a godsend.

I could write pages upon pages of what we've done, but the RPi Fatdog blog has a great article on the subject

Using just one Raspberry Pi and a reliable RTC (real-time clock) module you can create an inexpensive time server for your network. The RTC they're referring to supposedly drifts about a minute per year; still not awesome, but alright. *

This setup works well and Windows servers will happily make use of it! Linux NTP clients and other, stricter NTP software will balk at the fact that your Stratum-1 box was never synchronized with another time source. This is proven by the ntpdate command refusing to sync:

$ ntpdate timeserver
4 Mar 12:27:35 ntpdate[1258]: no server suitable for synchronization found

If you turn on the debugging output for ntpdate, you'll see an error that the reference time for the host is in 1900, which is the Epoch time for NTP. The example below shows reftime (though not in 1900):

status=0664 leap_none, sync_ntp, 6 events, event_peer/strat_chg
system="UNIX", leap=00, stratum=2, rootdelay=280.62,
rootdispersion=45.26, peer=11673, refid=,
reftime=af00bb42.56111000  Fri, Jan 15 1993  4:25:38.336, poll=8,
clock=af00bbcd.8a5de000  Fri, Jan 15 1993  4:27:57.540, phase=21.147, freq=13319.46, compliance=2

The quick and easy work-around for this issue is to simply create both Stratum-1 and 2 in-house :) Have one RPi run as S-1, with 2 or 3 RPis working as S-2, that sync their time off the S-1 and who are peered among themselves. Any NTP client will then happily accept your S-2 boxes as NTP source. 

Better than nothing! And cheap to boot. 


*: Remi Bergsma wrote an interesting article about Raspberry Pi clock accuracy, with and without RTC. tags: , ,

View or add comments (curr. 0)

MacOS, Steam and legacy controllers

2017-06-27 06:39:00

Ten years ago, almost to the day, we bought a Playstation2 to play rhythm games like DDR and Guitar Hero. The console and its games have long since been relegated to storage, but one of the DualShock controllers is still with us in the living room. Our friend Baris once gifted us a LikSang SmartJoy Playstation2-to-USB converter, which I've been using in OpenEmu to play classic SNES games with Dana. 

In this month's Steam Summer Sale I grabbed two great games, "Ori" and "Hollow Knight", which play better using a controller. Unfortunately they don't recognize the SmartJoy out of the box, so I had to do some research. "JoystickMapper" to the rescue! It'll work with just about any controller and can be used to map buttons to keyboard actions, which most Mac and PC games support. Now I won't have to shell out bucks for a new controller! /o/ Well worth the five euros for JoystickMapper. tags: ,

View or add comments (curr. 0)

Starting something new - SLAE: SecurityTube Linux Assembly Expert

2017-06-22 19:48:00

The ecstacy of achieving the OSCP certification didn't last long for me. Sure, I'm very happy and proud that I passed, but not two days later I was already yearning to move on! I wanted to get back to the PWK Labs, to finish the other thirty-odd servers. I wanted to retake the exam a second time. I wanted more challenge! So I set to making a list!

As something inbetween, I've signed up for SecurityTube's SLAE course: they teach you basic x86 assembly programming, to build and analyze Linux shellcode. Sounds very educational! And at only $150 for the course and exam it's a steal! I'll be blogging more about this in the future :)

Signing up for the course went easily and I got all the details within a day. However, actually getting the course files proved to be a struggle! There are three ZIP files, totalling roughly 7GB. They're stored in Amazon S3 buckets, which usually implies great delivery speeds. However, it seems that in this case SecurityTube have opted not to have any edge locations or POPs outside their basic US-WEST location. This means that I was sucking 7GB down a 14kbps straw :( That just won't do! Downloads were horribly slow!

After doublechecking that the issue did not lie with our home network, I attempted to download the files using my private server in the US: speeds were great. However, downloading from my own server wasn't much faster. Darn. Maybe there's another hickup? Two of my colleagues suggested using a VPN like PIA; sure that's an option. But I've been meaning to look into Amazon's AWS service, which allows you to quickly spin up virtual machines across the globe, so I went with that. 

I built a basic Ubuntu server in Frankfurt and downloaded the files from the US. Seeing how both the source and destination were on Amazon's network, that went perfectly fine. Grabbing the files from my Frankfurt system also went swimmingly. So after two days of bickering I finally have the course files on my laptop, ready to go :) tags: , , ,

View or add comments (curr. 2)

OSCP: more questions

2017-05-25 18:12:00

Here's another question I've had a few times, which came to me again this weekend:

"I'm really surprised you had the confidence to tackle the exam with just 19.

Is this you bread and butter ? Was this simply to formalize existing knowledge for you ?"

To be honest, I was just as surprised that I passed! No, I don't have workexperience in the field of pen-testing; I've only done two or three CTFs.

My original intention with my exam was to consider it a recon missions for my second exam. I was sure that 19 out of 55+ hosts was not enough to be prepared for the exam. I went into the exam fully reconciled with the idea that failing was not just an option, but all but assured. The exam would be a training mission, to learn what to expect. 

The day before my exam I had practiced exploiting a known buffer overflow in EasyRMtoMP3Converter (EXE). Here's the CoreLan writeup from 2009. Using the approach I learned during the PWK class and by studying various published exploits, I built my own Python script to exploit the software. After some additional work, the code worked against both Windows 7 and XP. 

This extra practice paid off, because I managed to finish the BOF part of the exam within two hours. This was basically the wind in my sails, what got me through the whole exam. After finishing the BOF I dared to hope that I might actually have a chance :) And I did. tags: , ,

View or add comments (curr. 0)

OSCP: Is the Pentesting With Kali (PWK) course worth it?

2017-05-23 14:07:00

One of my past colleagues reached out to me today, asking me this:

I'm still OSCP-wannaby, but probably it is too technical for me. I'm still not sure. Could you please share if a pre-exam training is worth its price or what is your practical - cutting of 'try harder' ;-) - advice to pass it?

I'll post my reply here, because I've been telling people this very thing for the past few weeks.

I've always thought OffSec's online PWK training to be well worth the money! $1150 gets you a huge PDF with all the course work, a few hours of videos and 90 days of lab access. It also includes your first exam attempt. For a training of this quality, that's really not a lot of money! You could even opt to pay even less, getting only 30/60 days of lab access.

The classroom variant is something else entirely though. It's a LOT more expensive, at roughly $6000. That's for a week's on-site training, including a CTF event on one night. You also get the same PDF and videos, the included exam, but only 30 days of lab access. For me, it was well worth it because it was five days of non-stop hacking in a room with 30 other students and two top-notch trainers.  

Something that saved me time and money: during the classroom training you receive the two most important VMs, which you can use on your OWN laptop. Thanks to that, I didn't have to start my lab access until I'd finished >90% of my exercises. In the online PWK you use lab access to work on your exercises!  

The course is always worth it before taking the exam: submitting a proper report of your coursework may net you 5 bonus points on the exam. Submitting a pen-test report for the labs may net you a further 5 bonus points. On a minimal passing score of 70, those 10 points can really help a lot!  

So yeah. Definitely work through all the coursework to get into it and score points. Then play a lot in the labs, for both practice and more points. Then take the exam when your time's up. Always do the exam! Because if you fail your exam and then renew your labs, OffSec will include a "free" retake of your exam with the new lab time! Totally worth it! That way your "failed" exam because a recon mission that teaches you a lot! tags: , ,

View or add comments (curr. 0)

Hooray for Google's free projects

2017-05-11 21:04:00

A few weeks ago, I reopened commenting on this site after having it locked behind logins for years. Since then the amount of spam submissions have been growing steadily. Sucks, so I finally took the time to implement proper spam checking. Enter Google's free project reCaptcha. Of course I realize that, if something's free on the web, it probably means that I'm the product being sold. I'll have to poke around the code to see what it actually does :)

CodexWorld have a great tutorial on getting reCaptcha to work in a basic script. Took me less than an hour to get it all set up! Lovely! tags: ,

View or add comments (curr. 3)

I love Microsoft's documentation!

2017-05-09 10:24:00

Four Windows servers on one laptop

A bit over a year ago I first started working with Microsoft's Active Directory, integrating it with BoKS Access Control. At the time, I was impressed by Windows Server 2012 and 2016 and the ease with which I could set up an AD forest with users. 

I'm now learning how to build a two-tier PKI infrastructure, after seeing them in action at various previous clients. I've been on the consuming end of PKI for years now and I thought it was time to really know how the other end works as well! I must say that I love Microsoft's generosity when it comes to documentation! Not only do they provide proper product docs, but they also have online tutorials in the form of TLGs: test lab guides. Using these, you can self-teach the basics of a subject, and then build up from there.

The 2012 Base TLG helps you build a basic AD forest of systems. I can follow it up with the two-tier PKI infrastructure TLG, which helps me set up an offline root CA, and an issuing CA, along with automatically enrolling any new systems in the networkt that need SSL certs. Awesome!

I'm similarly extatic about the performance of my Macbook Air. It's a tiny, super-portable system, but it still doesn't balk at running my usual applications plus four full-fledged Windows Server 2012 hosts. Nice!


Ammar Hasayen also did a nice write-up, which appears to be based upon the two-tier PKI TLG but which adds additional details.

Also, Microsoft also offer a third great resource, their MVA: Microsoft Virtual Academy. They also have a course on two-tier PKI with ADCS tags: , ,

View or add comments (curr. 0)

Older blog posts