Paranoid Penguin - Get a Clue with WebGoat

As more and more critical applications have adopted Web browser front ends, Web security has become the most critical front in Internet security. And yet, year after year, the same types of Web application security mistakes keep cropping up in security bulletins: SQL injection, cross-site scripting, authentication mechanisms that “fail open” and so forth. How, as a Web developer or administrator, can you avoid making these mistakes with your own Web applications?

The WebGoat can help. Developed by the Open Web Application Security Project (OWASP), the WebGoat is an “intentionally insecure” Tomcat Web application that walks you through common Web security mistakes, exploits and solutions. In this article, I explain how to install WebGoat on your Linux system and use it to educate yourself on Web application security.

The WebGoat on Linux has a critical dependency: the Java 1.5 Software Development Kit (JDK 1.5). Therefore, make sure you've installed your distribution's package for the JDK 1.5. On SUSE and OpenSUSE systems, this package is called java-1_5_0-sun-devel. On Debian and Debian-derived distributions, like Ubuntu, it's called sun-java5-jdk. Note that Red Hat and its derivatives don't have their own JDK 1.5 packages; see Resources for links to two articles that may help.

Your JDK 1.5 package's setup script should set your JAVA_HOME environment variable to the JDK's root directory. (On my OpenSUSE system, this is /usr/lib/jvm/java, which is actually a series of links to /usr/lib/jvm/java-1.5.0-sun-1.5.0_12/.) You may need to log out and back in for this variable to “take”, but regardless, it must be set correctly for WebGoat to run. If in doubt, do an echo $JAVA_HOME from a bash session to check to see whether it's set correctly.

Note that you do not need Apache installed to run WebGoat. In fact, if it is installed, I recommend you shut it down. WebGoat runs on its own bundled Tomcat installation, so although Tomcat is required, you don't need to install it separately.

To get the latest version of WebGoat, go to either WebGoat's SourceForge Web site (sourceforge.net/project/showfiles.php?group_id=64424&package_id=61824) or its Google Code Downloads site (code.google.com/p/webgoat/downloads/list). Along with the Windows releases of WebGoat, you'll find the standalone Web Application Archive file (WAR) version of WebGoat for UNIX/Linux and the “Release” version that includes Tomcat. You should opt for the latter, unless you've already got a working Tomcat installation on your system.

On my OpenSUSE system, I unzipped the Release version (Unix_WebGoat-5.0_Release.zip) in my home directory, which resulted in a new subdirectory, WebGoat-5.0 (/home/mick/WebGoat-5.0/). This directory contains a readme file (readme.txt), WebGoat's startup script (webgoat.sh) and another directory, tomcat, that contains the Tomcat servlet engine plus, of course, the WebGoat WAR file.

Now that you've installed WebGoat and the things on which it depends, but before plunging into Web-hacking mayhem, there's one other thing you need: a good graphical local Web proxy. Not a proxy server like Squid; rather, a local proxy you can use to intercept, view and alter the data your Web browser sends to Web servers. This is a critical tool in the Web hacker's bag of tricks—it's also very useful for Web developers who need to troubleshoot their own Web applications—and you'll need it to complete many lessons in WebGoat.

OWASP recommends the official OWASP proxy, WebScarab, which is available at www.owasp.org/index.php/OWASP_WebScarab_Project. WebScarab is a free, full-featured Web proxy and spider (a spider follows all links on a Web site, effectively cataloging it), all with a convenient GUI. It's also written in Java, which means it's cross-platform.

WebScarab can be downloaded as either a “self-contained” JAR file (Java archive) and run with java -jar ./webscarab-selfcontained-20070504-1631.jar or as an installer (currently webscarab-installer-20070504-1631.jar) that, when executed via the command java -jar webscarab-installer-20070504-1631.jar, unpacks WebScarab into the WebScarab directory in your home directory and installs a shortcut in your KDE or GNOME start menu. Start WebScarab either via this shortcut or by executing the self-contained version with the java -jar command.

Another good graphical, Java-based local Web proxy is Paros, available at www.parosproxy.org/index.shtml. Maybe I'm just more familiar with it, but I prefer Paros' interface. In my opinion, it's a little more friendly to non-expert users. You be the judge—both WebScarab and Paros are free, so there's no reason not to give each of them a spin.

Paros comes in the form of a zip file that decompresses to the directory paros. Inside, among other things, are a couple different versions of a startup script. The one you want is called startserver.sh. Start it with the command sh ./startserver.sh.

Note that you don't need to be root to install or start either proxy. In fact, there's no good reason for you to be root, because both proxies, by default, listen on the unprivileged port TCP 8008. You can change the listening port in WebScarab's Listener tab or in Paros' Tools→Options→Local proxy screen.