SANS Penetration Testing

Part 2: Quick and Useful Tricks for Analyzing Binaries for Pen Testers

[Editor's Note: In his previous blog post, Yori Kvitchko provided a bunch of tips penetration testers could use to analyze binary files, focusing on network communications. This time around, Yori looks at application data files, a hugely important source of information that could include passwords, hashes, or other sensitive stuff leaking out of an application. The techniques Yori describes here are some important building blocks for all pen testers to apply to the applications we analyze. -Ed.]

by Yori Kvitchko

This blog post is the second in a series of three blog posts dedicated to quick and useful techniques for analyzing binaries. In my first post, I talked about how penetration testers and other analysts can find and isolate network traffic generated by a binary. This time we'll look at pillaging the various data files that binaries and applications leave lying around. Our focus will again be on the Windows side of things, as that's where we often find the juiciest applications to analyze, including client-side software and internal tools.

In Windows, application data files are often placed in the AppData folder. This folder, specific to each user, can be a gold mine of information about installed applications. Located in each users' home directory, AppData (Application Data on Windows XP) can be accessed using the %AppData% environment variable, as in "dir /a %AppData%" (I put in the /a after the dir command to show folders with any combination of attributes; sometimes items in the AppData directory have a hidden attribute, so we want to see all them with dir /a).

Here are some useful files to keep an eye out for:

  • History, Cache and Temporary Files - The prime example here is anything related to a web browser. Many applications take advantage of Internet Explorer for browser windows inside of the application, so IE cache and temporary files can prove insightful about the activities of the user and may hold sensitive, leaked information.
  • Configuration Files - Anything from IP addresses to passwords might turn up here.
  • Saved Data Files - If the application in question has a saved data file format, these saved data files can often contain useful information in the data as well as the meta-data.

To analyze these application files, as well as any files found in the application's main directory, we can employ a number of different techniques. First and foremost, our good friend, the strings command, proves to be just as useful in analyzing data files as it is on binary files. Be on the lookout for the same type of data we talked about in the first blog post, URLs and IP addresses especially. Strings is freely downloadable for Windows from Microsoft Sysinternals. It's also worthwhile noting that the Sysinternals strings looks for both ASCII and Unicode strings by default, returning sequences of three characters or more in length.

Once we have some files on our hands, and we've done some cursory analysis with strings, we've likely either encountered a cleartext ASCII file (XML is especially common!) or we have a binary data file on our hands. If that's the case, we have two easy-to-use sources of information to help us identify the type of file. The file extension itself (such as .asc, .xml, or .docx) and the Linux "file" command. The file command can also be downloaded for Windows from GnuWin32. We can use it as follows:

$ file data.ext

data.ext; gzip compressed data, from Unix, last modified: Mon Mar 11 14:35:58 2013

Let's take a look at some of the more common data file formats we run into and how to extract data from them.

zip/tar/gzip - Decompress with the zip program of your choice. These files usually contain another data file inside. Many data formats are actually zip files in disguise. It's always worth trying to rename a file to ".zip" and try to unzip it just to check.
plist - Property list files used by Mac OS X and iOS. These files are especially useful when analyzing a mobile app. You can use a tool like plist Editor (http://www.icopybot.com/plist-editor.htm) to view the contents of the file.
sqlite - Sqlite databases are sometimes used for local data storage (as in Firefox and many mobile applications). Use SQLiteSpy (http://www.yunqa.de/delphi/doku.php/products/sqlitespy/index) or the Linux tool sqlite3 to view the contents of the database.
swf - Not exactly a data file format, but swftools (http://www.swftools.org/) does a great job of extracting images, sound, video, and even source code from SWF Flash files.
General Metadata - For general metadata, not specific to any file type, use ExifTool (http://www.sno.phy.queensu.ca/~phil/exiftool/) to see all metadata attached to a file. Images and documents are especially good sources for valuable metadata.
File System Images - Although not strictly a data file created by applications, we as security practitioners often have the need to work with file system images and some developers can occasionally get pretty crafty. Check out AccessData's FTK Imager (http://www.accessdata.com/support/product-downloads) for mounting all manner of file systems.

If the file format isn't in the above list, Google is a great resource for finding tools to analyze specific file types. If all else fails, see if a local installation of the application that created the file can be used to read it and extract its data. A great example of this would be copying a Firefox profile locally and importing into a local Firefox installation to view cookies and history.

In our next (and last) installment of this blog post series, we will look at some simple techniques for decompiling executables and DLLs to give us that last bit of insight we might need. After all, what could be more juicy when analyzing a binary than being able to peer right at the source? Until then... signing off —

-Yori Kvitchko
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