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Bosses love Excel...hackers too!

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Bosses love Excel...hackers too!
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Remote applications published in companies are around us in the cloud. In this talk we are going to add ICA and Terminal Server Apps to fingerprinting process, automating data analysis using FOCA. It will allow attacker to fingerprinting internal software, internal networks and combine the info in PTR Scanning, evil-grade attacks and command execution trough Excel files. In the end, we are going to play with a tricky feature in security policies about remote excel that will allow hackers to bypass macro restrictions. Chema Alonso is a Security Consultant with Informatica64, a Madrid-based security firm. Chema holds respective Computer Science and System Engineering degrees from Rey Juan Carlos University and Universidad Politécnica de Madrid. During his more than six years as a security professional, he has consistently been recognized as a Microsoft Most Valuable Professional (MVP). Chema is a frequent speaker at industry events (Microsoft Technet / Security Tour, AseguraIT) and has been invited to present at information security conferences worldwide including Black Hat Briefings, Defcon, Ekoparty and RootedCon - He is a frequent contributor on several technical magazines in Spain, where he is involved with state-of-the-art attack and defense mechanisms, web security, general ethical hacking techniques and FOCA, the meta-data extraction tool which he co-authors. Juan Garrido "Silverhack" is a forensics professional who had been working as security consultant the last seven years. He is the writer of two books about Forensic Analysis in Windows Environments and actually works as security consultant in Informatica 64.
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Transcript: English(auto-generated)
Hello. Hello, everybody. How many of you speak Spanish? Okay, perfect. Well, we got here a trophy because today, this morning, we had a tournament of soccer and our team won the trophy. The Spanish team, the FOGA team, I'm sorry for Argentina and South Africa, the
rest of the team, we won the trophy. Next year, maybe. Well, thank you for coming to this session. First of all, let me introduce to us, my friend is Juan Garrido and I'm
Cem Alonso. We are working in a small company in Spain called Informáriga64 and before that, before starting with the topic, we would like to introduce our country. We are from Spain. Probably, it's a small country. This is a small country in the middle
of everything. We are in the middle of Europe and Africa and South America because of our history and if you never went to Spain, you have to go there. I'm from Madrid, which is a very nice city. It was the capital of the big empire five centuries ago. But it's
a very nice city and if you go to Madrid, you will never be a foreigner because if you go to Madrid, you are from Madrid, so come to our city. Juanito is from another city. It was the capital of the Arabic empire in the seventh century when Spain was an Arabic country a lot of centuries ago and from that tower is the gold's tower, the first tower
on the left, is where the gold from America came to Europe. That's the gold's tower. It's on Sevilla and Sevilla is very famous because of the parties, because of the government and so on. And especially, there are big monuments. This is one of the most
famous monuments in Sevilla. It's the Plaza de España. Probably, all of you know this monument and you have to visit it because it's a monument in which you will fall in love because if Anna Kina Skywalker fell in love in Sevilla, you can do it also. So
don't forget to visit our country. Well, Juanito is from a very small area of Sevilla, which is Triana. Triana is an independent republic in Sevilla and it's very famous for the Holy Week because they are very religious and there are thousands of people carrying
the images and of course, after that, having drinks. Well, we work in Informatica 64 and probably, some of you have been listening about FOCA, which is one of the tools that we
develop and it's a free tool that you can use for strike information, pen testing and so on. Tomorrow, we are going to deliver a workshop of eight hours with a new version, which is the version three. So if any of you want to attend, I'm not sure if you can book for a seat, but you can ask for it. What is the topic that we are going to talk
today? Well, we are going to talk about something which is very common, which is the remote application using Citrix and terminal services. There are a lot of work done previously about this topic, about Citrix application and Windows terminal services, but we still
believe that it is important because nobody is taking care about it and nobody. A lot of people have a secure environment and we are going to see how easy a hacker can get into a company just using this kind of environment. So first of all, it's very easy to
discover the entry point of a company just searching for remote application or remote connection on Google. Just searching for RDP files, you can discover almost 2,000 places, almost 2,000 servers publishing applications. Of course, you can discover also government
sites, government with remote application that you can just click on it and test it. We'll see what happens. Well, you can do the same, more or less the same in Bing. In Bing, you cannot use the extension modifier, but you can use the file type. This is a
TXT file and searching for any of the modifiers which appears in all the files, you can discover thousands of remote applications. So some of the places that we discovered with this remote application are from the government. This is one of the sites, the
patrol order management system. It's a .mil domain here in the States, but we were going to do a demo with this server, but we were talking to Jeff and Jeff phoned something, someone, and today it's fixed. I don't know why. But we are going to do the
demo with the California transportation, the Department of Transportation, which is another site. Well, just reading the websites, you can discover the remote application. There is a NICA file and you can download the file and just click on it and
see what happens. I promise five minutes ago it was working. Five minutes ago it was
working. Maybe most was fun. Well, no problem. We are going to do the next demo. Don't worry. Well, as we are going to see, there are a lot of things to worry about and
it's very complicated to secure all the environments. This picture with the demo doesn't make sense. Sorry. Sorry. Are you sure? No. I don't learn it five minutes ago.
Okay. Let's download it again. But we downloaded it five minutes ago. California,
transportation, routing database, here it is, call trans. No, no. They fixed it. Five
minutes ago it was working, believe me. Well, don't worry. Well, one of the biggest problems with these files, these configuration files, is the verbosity. Just reading the files, which are TXT files, you can discover a lot of crap information, like internal IP address, users, encrypted password. You cannot use that password. You
can extract the password from the encrypted password, but you can get access to the system using an anonymous account or a user account in the system. So these files are perfect for the people who is collecting information or for some special attacks, like the
evil great attack. Just searching on the Internet for this kind of files, just searching for an ICA file, you can search for X ICA and just search for ICA files.
Documents with RNT, you can discover files with the password for Oracle just in the text. So you don't need to do any special. There are a lot of information in that file. So due
to this, we decided to add this kind of files to FOCA, which is our tool for information gathering and for fingerprinting information about websites and companies. Right now, if you don't load tomorrow, the FOCA 3 version, you will see that in the new
version, FOCA is searching for this kind of file and extracting information and so on. The second big problem is that it's a TXT file, so whoever has the file can modify the information and can try to get access to another part of the operating system. So just
modify the configuration file and generating error messages on the server, you can discover something like all the application in the operating system. You only need to create a logic with the error messages and terminal services and server has different error
messages when you cannot get access to the file than when the file is not on the server. So just trying to ask for applications, you can extract the whole list of applications
installed in a computer. To do this in terminal services is quite simple because there is a modifier which is alternative shell. This option was created for versions of the RDP protocol previous to version 6, but it exists still in the RDP files of terminal service
2008. It doesn't work, but the option, it is there. So you can ask for an application and the terminal server will say, okay, you cannot access this program because the alternative shell is forbidden. But you will receive different error messages. So if you receive, which is in Spanish, you know that the file is in the
operating system. But if you receive, you cannot get access to this file, you know that this file is not in the server. So the good thing is that you can do the same in
Citrix and there is any protection against one connection, another connection, another connection and you don't have even to type a capture. So you can optimize this procedure with a tool we created, Kaka, which is computer-assisted Citrix apps. And it's
just a tool to do this. So you only need to open Kaka, select one IK file, a list of
break edits, command, no exits and calc. And Kaka and the number of threads that you want to use in parallel and Kaka will do this for you. So you can go to have a coffee. Kaka is
working. Kaka is working. Well, Kaka is trying to open the application and the only thing that Kaka is doing is having a snapshot. So then, when Kaka finishes, you only have to review the error messages. So, of this way, you know if the application exits or not.
You can use a very big list of applications and leave Kaka running on a computer for one day and at the end of the day, you'll get your list of applications in Kaka.
The other thing with terminal application is what we call playing the piano. In the terminal services environment and Citrix environment, there are too many links, too many
environment variables, too many shortcuts, too many options that allows to a hacker to get a special part of the system that the system administrator didn't think about at the beginning. One of our favorite is Windows Server 2008 because Windows Server 2008 wants to help you everything. So if you ask for an application which is not in the operating
system, Windows 2008 shows you an error message with a help button. Would you like help? Why not? So just clicking on help, the help application appears and in this
application, you got a lot of links to open Internet Explorer or to open the open file panel and run commands and so on. Playing the piano was a very nice thing to do with a lot of shortcuts to access different parts of the operating system, but right now, we got more and
more shortcuts, sticky case, which is a funny thing, just clicking on shift K three or four times, the operating system will show you the sticky case menu, which is within the control panel, so even if you don't have access to the control panel with the sticky
keys, you will be able to configure all the control panel of the operating system, just clicking on shift and so on. It's easy to do this. Well, let's do a demo with the, a demo with Citrix. Well, this is the website of Citrix, but you can see it
this is the website for demo servers, so it's a demo, it's legal. We got a user here, which is Tonto Del Culo, the Spanish name. The rest of the user name was taken. No. No, no, no, no.
No, no, no. No, it is working. Well, this is the environment, as you can see in this
environment, we got a lot of applications. We are going to use Excel, because this talk is about Excel, so let's go to the office application and run Excel. Excel is working. Well,
Excel is working. Well, right now, the system is downloading the client components, so open Excel. Launch. You have to open launch. No? Maybe. No, no, no. Execute. Okay. Launch.
Well, something with Internet Explorer, but we are going to launch the Excel. Excel is
working, believe me. Start in Microsoft Excel. Internet is slow. No, man. Are the
weapons working? Where is Excel? Oh, my God. Okay, it is working, at least, in the end.
Well, now connect to the remote Excel. Come on. Please, if someone is doing a man-in-the-middle
attack in this network, please, don't do it. What happened with the Internet? In
English. Hey, just open Excel. We didn't do anything. Okay. Open. Well, this is the
Citrix environment. It is supposed to be secured by the guys of Citrix, so let's try to, I don't know, use the environment variable to connect to the system root. It's forbidden to the user profile. It's forbidden, and so on, but you can do a lot of
tricks. One of the tricks that we did was just to create a shortcut to the command, finish, all files, and then run. Open. Open. Open. Open. Open. Open. Open. Open. Open.
Ah, they fixed it. No, power cell. Too many consoles. Too many consoles. Power cell. Let's change. Now we are going to use another console. Same trick, another console.
Open. It is working. Go to the. And you get access to all. It's very complicated, because every day the operating system is getting more and more complex, and the
application that we are publishing through N are more and more complex. Please stop, stop, stop, stop, stop. Don't trust in people from Sevilla, believe me. Well, the
question is that the operating system is more and more complex, and the application are getting more and more complex, so every application that you are publishing through terminal services is a path to your operating system or through terminal services. One of our favorites is the complex application, and of course Excel is one of the most
complex applications that companies are publishing through remote application services. So, the good thing is that Excel is a very powerful tool, and bosses love Excel, because you can do a lot of funny graphics and analyze a lot of data, connect Excel to
databases, perform data mining, and a lot of things, which are very good for the business. And the good is that to do all that funny things, you need visual basic for applications. If you remove visual basic for application from your Excel, your Excel
becomes another kind of application, but Excel no more. So the idea is that with Excel, you can do a lot of things. Let's do the first demo, just in local. We got a Windows 2008 with Hyper-V, no, with terminal services, sorry, and in this
environment, we published Excel 2007. We didn't use Excel 2010, because the security policy for macros are more or less the same. The main difference in Office 2010 and Office 2007 is about the sandbox, about the security option when you
download a file from an unsecure location from the internet and so on, but once you have the file in your machine, in your computer, the security policies for macros are the same. So, in this environment, we are going to execute just an Excel with
Excel. It's going to be executed in your local machine. The security option by default is that the user selects if he wants to execute the macro or not, because the user is running the macro on his machine. But in a terminal service environment, a remote
application environment, the security option by default, which is case by case, the user decides it's a bad option, because the user is running the visual basic for applications, not in their machine, but in the shared machine, which is completely different. In this environment, we are going to execute just a file with visual basic
for applications. It is working. Well, in the example, we created a panel, and this is
the by default option. The user decides, okay, enable this content or not, okay, enable. It's not my machine. So, now you can, if the boss came, you can show the graph. It's a good trick. Then open the panel. So, just, you can do a lot of things with
visual basic for application, for instance, see the process, and so on. As you can see, close, through the Windows management instrument station, you can, through commands, retrieve the results, and so then on the Excel file. Okay, let's close it. So, we go back to
the presentation. Well, after seeing this demo, it's clear that you have to take care about the security of Excel in remote environment. One of the first things that system
administrators tend to do is to block some special controls, like command con, like PowerShell, WMI, and so on. But there are too many console, and in Windows Server 2008,
the backup directories copy all those console, which it creates a double problem, because you have the double of consoles. But in this environment, we are going to have all the consoles forbidden. We've got using ACLs and using server station policies, we are going
to forbid all the consoles, as you are going to see, but we can use consoles even from other operating systems. This is a trick that was published by the D.R. Stevens, and the idea is that you can inject a DLL into your Excel file, and that DLL is a common
interpreter. So, just invoking the common interpreter from your DLL, you are going to have access to the server. So, let's do a demo with this. So, if we go to the Windows Server 2008 and try to execute command con, it is forbidden. But in the Excel
file that we are going to open, we've got a DLL of ReactOS and also a DLL for the registry editor of ReactOS. So, just open the file and open the common line. Now, the
Excel file is extracting the DLL to execute it, and we are going to obtain the ReactOS common interpreter. Actually working, I hope. Well, here it is. As you can see, we
got the ReactOS common interpreter, and it's like the common, like the command interpreter of Windows 2008, more or less the same. So, this is a good trick. So, go back to the slides. And, of course, in the tax manager, you cannot see the CMD because it's a DLL
which had been loaded by the Excel file. So, it's not in the tax manager. The user is only working with Excel, which is good for the company. So, go back to the slides.
So, of course, after seeing this demo, some of you could think, okay, we are going to disable all the macros for my machine. If you use the first policy, which is disable Visual Basic for application, it's for all Office applications, not only for Excel, it's
for Word, PowerPoint, Access, and so on. And, for Excel, you got four options. The second option is case by case, the user decides. Of course, if the user is the attacker, it's an unsecure option. The third one is no macros at all. So, in this demo, we are
going to select the no macros at all in an Excel file published through a remote environment. So, we go to the Windows 2008 and select. We are going to log off the
connection of the user. Okay. And now, we go to the policies and we are going to enable the policy and select no, no macros, no warnings for all macros. The third one, no warnings for all macros, but disable all macros. Okay. No warning and macros off. So, select
that option. Okay. Apply the policy. Okay. Active Directory is working. Okay. So,
go back to the client and open the file. And, this is one of my favorite tricks. So, when you open the document, when the document is open, you will see how it's impossible to
execute anything because everything is forbidden. Try to do anything? No, it's forbidden. You cannot do anything. But, there is something special with Excel. There are trusted locations. A trusted location is a path in which security policies are not
applied. So, you only need to save the document in a trusted location. And, of course, the trusted locations are in the user profile. So, let's save the document. We are going
to use a trusted location. You can have trusted location in the client machine or in the server machine. It doesn't matter. If the document is open from a trusted location, all the security policies will disappear. So, we are going to save in one of the most famous trusted locations, which is the default book. When you open a new file, there is
something. Close. And then, open the document from the trusted location. Here it is. Well, no
markers at all. It's not markers at all. Well, after seeing this demo, there is a solution. No trusted location at all. Well, after seeing this demo, maybe the system
administrator can trust in digitally signed macros. Only macros that have been digitally signed for a trusted certification authority. So, let's do a demo with this. In the next example, we are going to select the four options. Remember, first option, all macros.
Second option, case by case. Third option, no macros. And fourth option is only digitally signed macros. So, let's log out the data section. And then, we are going to go, go, go, go. Digitally signed macros. Okay. Okay. Apply. Okay. We can apply in
my sweeper. Meanwhile. Well, we got a digitally signed Excel file, but it's a self-signed Excel file. And we are going to obtain this message. Okay. Okay. Okay.
Well, we obtain a warning because it's self digitally signed. It's not from a trusted authority. You got help protecting me from a no content ban. There is a link. A link for
show signature details. So, just click on the link. Here is the digital certificate. So, if we go to view certificate and the certification path, we can discover the root of the
certification authority. And we can view the certificate of it. So, we can install the certificate because it's at user level. Perfect. Install the certificate. Next. It's at user level. So, no problem at all. And now, the message will change to enable this
content. And the last one is the funny one. This is very important because with this
option, you can start the third world war. Because in this example, we created a SIA that we installed right now. And if you install this SIA, every time you install
this document signed by this SIA will be okay. And in the digital certificate, there is a link for the CRL. And the CRL is a link that could be an HTTP link, an LDAP link, and an
HTTP link could be a SQL injection attack. So, if you install SIA and send an Excel file with a digital signed macro to someone relevant in the company and he or she opened the document, automatically the crypto will try to connect to the CRL. So, if you
discover, for instance, a SQL injection vulnerability in the core of China, for instance, and you can install one of these rogue SIA in one of the DHAs machines and
you send a file to a user which is working in that machine, you can discover who user are working in what machine using FOCA. You can start the third world war. Well, just kidding, but we are going to do the demo in logo. So, in this example, that trusted
authority has now the CRL. So, we are going to open a netcat and we are going to send the document to a user. In this environment, it's the same user, but the problem is that in remote application environments, there are a pool of users that are shared for the rest of
the user. So, we are listening and let's see if the query is okay here. Okay, as you can see, there is some message. Notice PHP ID five equal five sat down. Minus,
hello, Aurora. I don't know, whatever. So, in the end, as you can see, it's very complex. It's very difficult to harden an environment with remote applications. So, if you got a terminal services environment, publishing a lot of application or a citizen environment, the
first thing that you have to do is reevaluate the security of the whole environment, reevaluate the security of all documents. Of course, you have to trust that nobody, not anybody, because in some operating system, nobody could be dangerous. And be sure about
the application that you are publishing. One of the funny things that we discovered is that in terminal services, with the terminal services web access, a lot of administrators are using this option, which is hide in terminal server web access. That means that if you have a remote application published on your terminal services, this
application won't appear in the HTTP panel, but the application is still published. So, if you know the name of the application, you can connect to that application. And that's all. Thanks for standing here.