Pentesting Java EE web applications with LAPSE+

Just a quick tip for anyone doing a code review of a Java EE web application: LAPSE+ is a very useful tool to have in the arsenal, whether you’ve got the original source or just the JAR/WAR file.

In my case, the client provided me with a single .WAR file which contained the application. As it was a large application, I didn’t really fancy digging through everything manually with JD-GUI, although it is an excellent Java decompiler. I decided to take the opportunity to give LAPSE+ a try.

Here’s what  you’ll need:

You can also grab a PDF instruction manual for LAPSE from the same site. However, be aware that I found some of the information in there to be a bit misleading, e.g. needing a specific version of Eclipse. Also, don’t worry if your client provided you a project for a different IDE, such as IntelliJ IDEA – it doesn’t really matter.

First step is to get Eclipse set up. Drop the .jar file from the LAPSE+ archive into the plugins directory of Eclipse. (Re)start Eclipse, then go to Window -> View -> Other… and select the items relating to LAPSE+. A little toolbar should appear on the right with blue spherical buttons. These are your LAPSE+ windows.

Next step is to load your code into a project. This is split up into two parts, but if you’ve already got an Eclipse project for the site’s source code, you can skip the first part. Otherwise, you’ll need to extract the code from your archive and make a project for it. Start by loading the JAR (rename the .WAR to .JAR if needs be) into JD-GUI. It should decompile the archive and let you browse the code. Go to File -> Export all Sources, and save the resulting ZIP file somewhere. This archive now contains all your decompiled source code, split into directories based on the namespace hierarchy.

Now, go back to Eclipse and create an empty Java project, filling the wizard out with whatever values suit you. Once that’s created, go into the project explorer tree and find the src directory, then right click it and select Import. Select your newly exported ZIP file, and Eclipse will populate your project with your reverse-engineered source. Now right-click the project and select Build. In all likelihood, it’ll throw a whole load of errors due to imperfect decompilation – don’t worry, we don’t really care, because LAPSE+ can still function with a broken build.

Once you’ve got your project set up, go to the individual LAPSE+ windows and browse through what they found. You might need to manually refresh them to run through the checking process. In my case, I found about a 10:1 ratio of false positives, which isn’t actually too bad for code scanning. Within an hour or so of digging through the results I’d found a couple of concrete XSS bugs that I’d not spotted yet, plus a whole bunch of potential XSS bugs that I couldn’t immediately find vectors for, and a whole variety of other interesting stuff to dig through. It’s a really nice way to cut down a 400kLoC project into manageable target points.

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