Tuesday, August 9, 2011

NetSPI Blog » Echo Mirage: Piercing the Veil of Thick Application Security

In recent years web application security has gotten a lot of attention. The advent of easy to use web proxies has brought a lot of attention to SQL injection and cross-site scripting vulnerabilities, and developers have taken note. Thick application security/development, however, is lagging in that respect. You can pierce the veil yourself and witness the unprotected underbelly of thick application security, because I’m about to teach you how to use a useful tool called Echo Mirage. Echo Mirage is a versatile local proxy tool that can be used to intercept and modify TCP payloads for local Windows applications. It allows users to launch a program behind its proxy or hook into an existing process. It also supports OpenSSL and Windows SSL. Using this tool sheds light on a whole slew of bugs and holes concealed by the thick application security illusion.

Keep in mind that this technique could be interpreted as reverse engineering. Depending on the license of the software you are testing, this could stray towards the grey side of legality. For the purposes of this tutorial, I have created my own C# SQL command handler.

Step 1: Acquire Echo Mirage from here: http://www.bindshell.net/tools/echomirage. The official release version is only 1.2, and the demonstrated version is 2.0, which you can preview here: http://www.bindshell.net/entry/31.html

Step 2: Open up Echo Mirage, and click File-> Execute. Choose the .exe for your file, and click OK. Click on the green Go arrow, and your application should start. Phonebooks, invoicing, and ERP systems are common examples of applications which hook into a database and could be vulnerable to this sort of attack.

Figure 1: Having selected my target executable, the path is listed in black.


Figure 2: After launching the application, the red text demonstrates that Echo Mirage is intercepting traffic from the target process.


Step 3: Initiate a connection to a remote database; while my slapdash SQL interface has a button labeled “connect,” many applications will be less clear about when a connection to a database is created. When I start the connection, Echo Mirage intercepts all the packets that I’m sending to the database. Note that even though the connection string is available, many recent implementations of SQL will encrypt the password before it goes over the wire.

Figure 3: Connection strings! My favorite!


Step 4: Create a query. It will be automatically intercepted by Echo Mirage, and you can relay whatever malicious queries you want. In another application this step could be running a search, updating a record, or generating a report. When sending your request, one limitation of Echo Mirage becomes apparent: it is unable to change the size of the data sent. What this means for a potential attacker is that sending a larger query allows for more space when injecting. There is little worry of sending a query that is too large; if you have extra space at the end of your injection simply comment the rest out. 

Figure 4: This is the query as sent from my interface


Figure 5: Echo Mirage captures the request


Step 5: Now that you have the query captured in Echo Mirage, overwrite some characters to inject. Try not to disrupt the formatting and only overwrite characters that were actually part of the query you sent.

Figure 6: The edited query, prior to sending


Figure 7: The results of the edited query


I hope this demonstration hits home and proves the necessity of input validation and parameterized SQL queries, even in thick client environments. As tools like Echo Mirage mature, this type of attack will only become more common and more dangerous.

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This post from the netspi blog really helped me to give some additional information to developers who were not understanding the reason why we should move our fat client applications to a controlled terminal services environment before even thinking about becoming PCI compliant. Good stuff.

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