DeXSS -- Java program for removing JavaScript from HTML

The HTML world has moved on in the ten years since DeXSS was first written.

New technologies such as HTML5, CSRF, and CSP are unhandled.

DeXSS remains available only as an historical artifact.

Dynamic web sites which allow users to enter text content containing HTML are at risk for so-called cross-site scripting attacks (Wikipedia, Securitydocs) attacks.

A common approach taken to mitigate this risk is to allow some HTML content, but block content that is potentially harmful. One problem with a straightforward approach to blocking such content is that HTML parsing in browsers differs from the ideal, and nefarious individuals can take advantage of these differences to obscure content.

DeXSS uses TagSoup, an open-source HTML parser that attempts to mimic how web browsers work. TagSoup reads wild HTML and generates SAX2 events. DeXSS invokes TagSoup and follows it with a pipeline of SAX2 filters to remove HTML tags such as script and attribute values containing such scripts.

Status

DeXSS 1.2 is an Alpha release. You should be aware of the following issues:

• This release implements a blacklist approach, which has advantages over a whitelist approach, but also has inherent risks. There are still a number of known XSS attacks that DeXSS does not yet detect.
• DeXSS is agressive about removing style attributes that fail the CSS analyzer. There are probably other CSS attacks that DeXSS does not protect against.
• Elements that TagSoup thinks should be in the head are discarded by the default settings; changing the BODY_ONLY flag to allow head content will reduce effectiveness greatly. Consequently, DeXSS should not be used to parse entire user-provided HTML files, but only parts that are destined for inclusion.
• The output of DeXSS is intended for browsers, not for storage. As a result, some constructs may be overly verbose.
• Configurability and test suites are lacking.
• DeXSS does not specially handle any HTML5 elements or attributes not present in HTML4.

If you have an interest in working on these issues, please consider contributing to the project.

DeXSS API

DeXSS includes the following classes for direct use:

• Test, a command-line utility for testing XSS removal.
• DeXSS, which implements a string-to-string conversion of HTML, with XSS removal.
• DeXSSParser, which can be used directly as a SAX2 parser to produce SAX2 events from an input stream.
• DeXSSFilterPipeline, which can be used as a SAX2 filter if you have already used TagSoup to produce SAX2 events

Documentation

• LICENSE
• README.txt
• CHANGES
• JavaDoc

Source

Source is at https://github.com/leighklotz/dexss.

Download

Current Version

• dexss-1.2.jar
• dexss-1.2-src.zip
• dexss-1.2-docs.zip

How to build

1. Type ant dist -emacs

Dependencies

• dexss includes tagsoup-1.2.1.jar from http://tagsoup.info If you need to change the TagSoup version, edit the file etc/build/build.properties.
• dexss includes osbcp-css-paser-1.4.jar from http://github.com/corgrath/osbcp-css-parser If you need to change the OSBCP CSS Parser version, edit the file etc/build/build.properties.

How to test

1. Test for false positives

    java -classpath lib/tagsoup-1.2.1.jar:lib/osbcp-css-parser-1.4.jar:dist/lib/dexss-1.2.jar org.dexss.Test tests/benign/*.txt 
   

   or

    java -classpath lib\tagsoup-1.2.1.jar\;lib\osbcp-css-parser-1.4.jar\;dist\lib\dexss-1.2.jar org.dexss.Test tests/benign/*.txt 
   

2. Test for false negatives

    java -classpath lib/tagsoup-1.2.1.jar:lib/osbcp-css-parser-1.4.jar:dist/lib/dexss-1.2.jar org.dexss.Test tests/xss/*.txt 
   

   or

    java -classpath lib\tagsoup-1.2.1.jar\;lib\osbcp-css-parser-1.4.jar\;dist/lib/dexss-1.2.jar org.dexss.Test tests/xss/*.txt 
   

Other Similar Projects

If DeXSS does not meet your needs, see freecode.com for a list of similar libraries in other languages such as PHP and Perl.

Todo

• CSS analyzer is still not applied to style elements, only style attributes.

Warranty

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Copyright and License

• This software is released under Apache 2.0 License (see file LICENSE).
• Copyright (C) 2005, 2006, 2007, 2012 Xerox Corporation
• Copyright (C) 2012 Leigh L. Klotz, Jr.
• Portions of the file build.xml were derived from TagSoup http://tagsoup.info Copyright (c) 2007 John Cowan licensed under Apache 2.0.