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PvIB CTF 2017: pen.test event

2017-10-08 10:29:00

the scoreboard

For the third year in a row I competed in the PvIB CTF "Pen.test event", a Jeopardy-style CTF where contestants race to solve puzzles and small hacking challenges. Last year I didn't fare very well at all, but this time aroud things went great! The crowd was nice, my table companions were cool, it was great talking to Anko again and the DJ played awesome beats. I had a blast!

Around 1.5 hours into the competition I went to stretch my legs and get a drink, enjoying the fun we were having. Looking around, sipping on my cola I noticed something odd about the scoreboard! When I'd managed to grab my phonecam I'd already been surpassed by one team, but for at least a short while I'd managed to be in #4 out of the pack of 51 contestants. In the end I finished somewhere halfway , because greater minds than mine managed to keep on scoring points :)

pvib ctf scoreboard

Like before, the challenges were divided into various categories (shown above) and ranked from easy to hard, resulting in different scores per item. I finished the night with 100.000 points (3x10e3, 2x10e4, 1x10e3). I was so, so close on another 10k and 30k points which is why I stuck around until the very last minute!

Web:

  1. I let myself be fooled by the easy Web challenge for way too long. The challenge presented you with a SquirrelMail login page and the task to login and get their email. Assuming it was a veritable SquirrelMail, I assumed no easy software vulnerabilities would be found, so I resorted to password guessing. An hour before the end of the night, Anko asked me "When we start out web pen testing, what are the things you're taught first?". Me: "Well... I reckon... You mean XSS, CSRF and SQL Injection, right?" A: "Absolutely." Me: "Sonuvabitch...". Turns out it was NOT SquirrelMail, just a quick and easy SQLi exercise made to look like it. 
  2. This challenge sent you to an online calculator which would help the voting committee tally their votes, in this case a basic formula line which would return the outcome. Entering gibberish into the line would return a basic Python EVAL failure. Turns out that it was possible to run OS-commands through the EVAL calculation line, which let me list the remote files and to grab the required flag.
  3. Both this exercise and #2 were a bit slow to respond in my browser, so I turned to the Lynx text-based browser. This foregoes all CSS, which was being loaded from the Internet. This time around we were supposed to hack a voting system, to find out the vote-total for each candidate. I noticed that it was based on a JSP that got included by URL, so I downloaded it for further analysis. This code showed me that the voting process makes SOAP calls to retrieve candidates and to place a vote. I also gave me examples of the XML data needed for those soap calls. From here on out, my challenge was to find out how to get voting results instead! I haven't worked with SOAP a lot, but I know there had to be some way of querying the remote end for available procedures and commands. This is where I learned about WSDL, which gave me exactly what I needed: a description of how to request voting results. This needed a little bit more tweaking to the XML, because the candidates were identified by an MD5 hash that needed to be updated as binary data. Darn! Was this close to getting the whole challenge, but was a few minutes too late. 

Learning on the go was hella fun! I got to renew my experience with CURL calls and XML data and learned new things about SOAP. Nice!

Crypto:

  1. I'd figured out the positional encryption scheme for this challenge pretty quickly, as it was clearly based on jumping and looping through the ASCII table, based on a character's position. Despite this, I seem to have had some stupid mistake in my method, because my decrypted text was repeatededly rejected. Again, this close to cracking it, but too little too late. 
  2. We were provided with two enigmatic strings and an encrypted ZIP file. Had no idea how to proceed with this one just yet.
  3. We're provided with Python code for a home-brew crypto, as well as some sample data. Given enough time I'm sure I could have figured out the issue at hand, but in this case ${ENOUGH_TIME} would -GT 2d. So never mind ;)

Cracking crypto never was my strong point ;)

Forensics:

  1. We're given a .CRT certificate for a voting machine, which supposedly is fishing. Making it legible with the OpenSSL command line quickly shows the PvIB CTF flag.
  2. We're given a .DOCX file which was supposed to contain suspicious data. I simply used unzip to extract all the components files of the Word document and searched the various XML contents for the CTF flag. 
  3. We're given a .PNG image that supposedly contains hidden data. One ZSteg install later I have my flag. 

Fun challenges! Not too hard so far.

Misc.:

  1. A PDF file with some hidden data in it. Open the PDF with the viewer on my Kali box made it stand out as a fat blue box. Anko simply grepped for "-i pvib" through the strings-output of the PDF and fared just as well :)
  2. Oooff! I wish I'd had my wife with me! She's great at logical reasoning :) This challenge combined logic (determine whether persons A, B and C are lying or tell the truth), math (Fibonacci and Harshad numbers) and programming (because there's no plausible way of quickly solving the puzzle on paper). Seeing how I can't ever get my ideas straight with the liars/truthers, I skipped this one after about half an hour. 

What a great evening! Better yet, on the way home I managed to get on the Slam! night show and I won a DAB+ radio for our home! :D Awesome-cakes!


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WTF HP? Your M203dn laser printer defaults to open SNMP write?!

2017-10-04 18:13:00

screenshot from the web interface

We've just bought a new laser printer, mostly for my daughter Dana's schoolwork. Installation was a snap as both Windows and MacOS have made it a fool-proof process. MacOS even gave me a button labeled "Visit printer website"! Of course that's gonna pique my interest!

Yup, the HP Laserjet Pro M203dn (as it's fully named) has a wonderfully helpful web interface! By default, there's no username or password, there's no login prompt whatsoever. Just open for everyone to browse. Which is where I stumble upon the screenshot I'm showing above. Of course the SNMP community strings default to public/public. Why not? But who in the seven hells decided to make that SNMP daemon -writable-?! That's asking for trouble!

... aside from the "no username or password on the admin panel" of course. Ye gods! O_o

Oh and of course the certificate on the https web server was not signed by HP's CA. Because of course I wouldn't want to verify that nobody messed with the firmware or the certs on the printer. 

... *checks around* Yep, HP also don't have a bug bounty program. =_=


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EX413 prep: messing with FreeIPA, Apache Directory Studio and MacOS

2017-10-01 21:44:00

Messing with FreeIPA

In preparation for my upcoming EX413 examination, I'm mucking about with FreeIPA

FreeIPA is a easy-to-setup solution for building the basis of your corporate infrastructure on Linux. It includes an LDAP server, it sets up DNS and a CA (certificate authority) and it serves as Kerberos server. Basically, it's a light version of Active Directory, but targeted at Linux networks. Of course Linux can use AD just fine, but if you don't have AD FreeIPA is the next best thing.

IPA has come a long way over the past ten years. It might still not be fully featured, but it certainly allows you to setup a centralized RBAC platform, not unlike the BoKS product range I've worked with. BoKS offers more functionality (like a password safe and the possibility to easily filter SSH subsystems like allowing SCP or SFTP only), but it's also far from free. 

I'm currently doing exactly what EX413 exams want you to be able to do: install a basic FreeIPA environment, with some users and some centralized SUDO rules. It's the latter that was giving me a little bit of a headache, because I had a hard time figuring out the service account to use for the bind action. Sander van Vugt's training video refers to the service account uid=sudo,cn=sysaccounts,dc=etc,dc=ex413,dc=local, which does not appear to exist out of the box. 

This set me off one a foxhunt that lasted 1.5 hours.

Because this is a sandbox environment, I've set up one account as both the SUDO bind user in /etc/sudo-ldap.conf and in the ADS user interface. Both now work swimmingly! I can "sudo -l" as a normal user and I can mess around the LDAP tree from the warmth and comfort of my MacOS desktop :)

EDIT:

Well I'll be a monkey's uncle! That little rascal of a UID=sudo was hiding inside LDAP all along! I guess I really did make a mistake in my initial ldappasswd command :D Well, at least I learned a thing or two!

EDIT 2:

FOUND IT! The OID I showed up top has an "s" too many! I wrote "sysaccountS", while it's supposed to be "sysaccount". Ace! That's going to make life a lot easier during the exam :)  


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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! ^_^


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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):

ntpq>rv
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=128.4.1.20,
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.


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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.


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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 :)


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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. 


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