Thomas Springer found a vulnerability in GNUJSP, a Java servlet that allows you to insert Java source code into HTML files. The problem can be used to bypass access restrictions in the web server. An attacker can view the contents of directories and download files directly rather then receiving their HTML output. This means that the source code of scripts could also be revealed.
The problem was fixed by Stefan Gybas, who maintains the Debian package of GNUJSP. It is fixed in version 1.0.0-5 for the stable release of Debian GNU/Linux.
The versions in testing and unstable are the same as the one in stable so they are vulnerable, too. You can install the fixed version this advisory refers to on these systems to solve the problem as this package is architecture independent.
We recommend that you upgrade your gnujsp package immediately.