Category:OWASP AntiSamy Project

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OWASP AntiSamy Project
OWASP AntiSamy is a library for HTML and CSS encoding.

Introduction
AntiSamy was originally authored by Arshan Dabirsiaghi (arshan.dabirsiaghi [at the] gmail.com) of Contrast Security with help from Jason Li (jason.li [at the] owasp.org) of Aspect Security (http://www.aspectsecurity.com/).

Description
The OWASP AntiSamy project is a few things. Technically, it is an API for ensuring user-supplied HTML/CSS is in compliance within an application's rules. Another way of saying that could be: It's an API that helps you make sure that clients don't supply malicious cargo code in the HTML they supply for their profile, comments, etc., that get persisted on the server. The term "malicious code" in regards to web applications usually mean "JavaScript." Cascading Stylesheets are only considered malicious when they invoke the JavaScript engine. However, there are many situations where "normal" HTML and CSS can be used in a malicious manner. So we take care of that too.

Philosophically, AntiSamy is a departure from contemporary security mechanisms. Generally, the security mechanism and user have a communication that is virtually one way, for good reason. Letting the potential attacker know details about the validation is considered unwise as it allows the attacker to "learn" and "recon" the mechanism for weaknesses. These types of information leaks can also hurt in ways you don't expect. A login mechanism that tells the user, "Username invalid" leaks the fact that a user by that name does not exist. A user could use a dictionary or phone book or both to remotely come up with a list of valid usernames. Using this information, an attacker could launch a brute force attack or massive account lock denial-of-service. We get that.

Unfortunately, that's just not very usable in this situation. Typical Internet users are largely pretty bad when it comes to writing HTML/CSS, so where do they get their HTML from? Usually they copy it from somewhere out on the web. Simply rejecting their input without any clue as to why is jolting and annoying. Annoyed users go somewhere else to do their social networking.

The OWASP licensing policy (further explained in the membership FAQ) allows OWASP projects to be released under any approved open source license. Under these guidelines, AntiSamy is distributed under a BSD license.


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What is AntiSamy
OWASP AntiSamy provides:

This page shows a big-picture comparison between the versions. Since it's an unfunded open source project, the ports can't be expected to mirror functionality exactly. If there's something a port is missing -- let us know, and we'll try to accommodate, or write a patch!

Presentations
From OWASP & WASC AppSec U.S. 2007 Conference (San Jose, CA): AntiSamy - Picking a Fight with XSS (ppt) - by Arshan Dabirsiaghi - AntiSamy project lead

From OWASP AppSec Europe 2008 (Ghent, Belgium): The OWASP AntiSamy project (ppt) - by Jason Li - AntiSamy project contributor

From OWASP AppSec India 2008 (Delhi, India): Validating Rich User Content (ppt) - by Jason Li - AntiSamy project contributor

From Shmoocon 2009 (Washington, DC): AntiSamy - Picking a Fight with XSS (pptx) - by Arshan Dabirsiaghi - AntiSamy project lead

Project Leader
[mailto:arshan.dabirsiaghi@gmail.com Arshan Dabirsiaghi]

Ohloh

 * https://www.ohloh.net/p/owaspantisamy


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News and Events

 * [26 Sep 2017] Please update AntiSamy to 1.5.5 or later per CVE-2016-10006
 * [20 Nov 2013] News 2
 * [30 Sep 2013] News 1

In Print
This project can be purchased as a print on demand book from Lulu.com

Classifications

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= How do I get started? =

There's 4 steps in the process of integrating AntiSamy. Each step is detailed in the next section, but the high level overview follows:
 * 1) Download AntiSamy from Maven
 * 2) Choose one of the standard policy files that matches as close to the functionality you need:
 * 3) * antisamy-tinymce-X.X.X.xml
 * 4) * antisamy-slashdot-X.X.X.xml
 * 5) * antisamy-ebay-X.X.X.xml
 * 6) * antisamy-myspace-X.X.X.xml
 * 7) * antisamy-anythinggoes-X.X.X.xml
 * 8) Tailor the policy file according to your site's rules
 * 9) Call the API from the code

Stage 1 - Downloading AntiSamy
First, add the dependency from Maven:

org.owasp.antisamy antisamy

Stage 2 - Choosing a base policy file
Chances are that your site's use case for AntiSamy is at least roughly comparable to one of the predefined policy files. They each represent a "typical" scenario for allowing users to provide HTML (and possibly CSS) formatting information. Let's look into the different policy files:

1) antisamy-slashdot.xml

Slashdot (http://www.slashdot.org/) is a techie news site that allows users to respond anonymously to news posts with very limited HTML markup. Now Slashdot is not only one of the coolest sites around, it's also one that's been subject to many different successful attacks. Even more unfortunate is the fact that most of the attacks led users to the infamous goatse.cx picture (please don't go look it up). The rules for Slashdot are fairly strict: users can only submit the following HTML tags and no CSS: &lt;b&gt;, &lt;u&gt;, &lt;i&gt;, &lt;a&gt;, &lt;blockquote&gt;.

Accordingly, we've built a policy file that allows fairly similar functionality. All text-formatting tags that operate directly on the font, color or emphasis have been allowed.

2) antisamy-ebay.xml

eBay (http://www.ebay.com/) is the most popular online auction site in the universe, as far as I can tell. It is a public site so anyone is allowed to post listings with rich HTML content. It's not surprising that given the attractiveness of eBay as a target that it has been subject to a few complex XSS attacks. Listings are allowed to contain much more rich content than, say, Slashdot- so it's attack surface is considerably larger. The following tags appear to be accepted by eBay (they don't publish rules): ,...

3) antisamy-myspace.xml

MySpace (http://www.myspace.com/) was, at the time this project was born, arguably the most popular social networking site today. Users were allowed to submit pretty much all HTML and CSS they want - as long as it doesn't contain JavaScript. MySpace was using a word blacklist to validate users' HTML, which is why they were subject to the infamous Samy worm (http://namb.la/). The Samy worm, which used fragmentation attacks combined with a word that should have been blacklisted (eval) - was the inspiration for the project.

4) antisamy-anythinggoes.xml

I don't know of a possible use case for this policy file. If you wanted to allow every single valid HTML and CSS element (but without JavaScript or blatant CSS-related phishing attacks), you can use this policy file. Not even MySpace was _this_ crazy. However, it does serve as a good reference because it contains base rules for every element, so you can use it as a knowledge base when using tailoring the other policy files.

Stage 3 - Tailoring the policy file
Smaller organizations may want to deploy AntiSamy in a default configuration, but it's equally likely that a site may want to have strict, business-driven rules for what users can allow. The discussion that decides the tailoring should also consider attack surface - which grows in relative proportion to the policy file.

You may also want to enable/modify some "directives", which are basically advanced user options. This page tells you what the directives are and which versions support them.

Stage 4 - Calling the AntiSamy API
Using AntiSamy is easy. Here is an example of invoking AntiSamy with a policy file:

import org.owasp.validator.html.*; Policy policy = Policy.getInstance(POLICY_FILE_LOCATION); AntiSamy as = new AntiSamy; CleanResults cr = as.scan(dirtyInput, policy); MyUserDAO.storeUserProfile(cr.getCleanHTML); // some custom function

There are a few ways to create a Policy object. The  method can take any of the following:
 * a String filename
 * a File object
 * an InputStream

Policy files can also be referenced by filename by passing a second argument to the  method as the following examples show:

AntiSamy as = new AntiSamy; CleanResults cr = as.scan(dirtyInput, policyFilePath);

Finally, policy files can also be referenced by File objects directly in the second parameter:

AntiSamy as = new AntiSamy; CleanResults cr = as.scan(dirtyInput, new File(policyFilePath));

Stage 5 - Analyzing CleanResults
The CleanResults object provides a lot of useful stuff.

- a list of  error messages

- the clean, safe HTML output

- the clean, safe  which is reflected in

- returns the scan time in seconds

= Acknowledgements =

Contacting us
There are two ways of getting information on AntiSamy. The mailing list, and contacting the project lead directly.

OWASP AntiSamy mailing list
The first is the mailing list which is located at https://lists.owasp.org/mailman/listinfo/owasp-antisamy. The list was previously private and the archives have been cleared with the release of version 1.0. We encourage all prospective and current users and bored attackers to join in the conversation. We're happy to brainstorm attack scenarios, discuss regular expressions and help with integration.

Emailing the project lead
For content which is not appropriate for the public mailing list, you can alternatively contact the project lead, Arshan Dabirsiaghi, at [arshan.dabirsiaghi] at [contrastsecurity.com] or Dave Wichers at [dave.wichers] at [owasp.org].

Issue tracking
Visit the GitHub issue tracker.

Sponsors
The AntiSamy project is sponsored by Contrast Security.

The initial Java project was sponsored by the OWASP Spring Of Code 2007. The .NET project was sponsored by the OWASP Summer of Code 2008.

= Road Map = This section details the status of the various ports of AntiSamy.

Grails
Daniel Bower created a Grails plugin for AntiSamy.

.NET
A .NET port of AntiSamy is available now at the OWASP AntiSamy .NET page. The project was funded by a Summer of Code 2008 grant and was developed by Jerry Hoff. However, this version of AntiSamy has not been updated in a while.

This port is no longer under active development, and is looking for a few good developers to help make it feature-synchronized with the Java version. If it doesn't suit your needs, consider Microsoft's AntiXSS library.

Python
A port of AntiSamy to Python was attempted, but has been abandoned since 2010. Michael Coates suggests you check out project Bleach instead: https://pypi.org/project/bleach/

PHP
Although a PHP version was initially planned, we now suggest HTMLPurifier for safe rich input validation for PHP applications.

=Project About=

Project's Assessment
This project was assessed by Jeff Williams and his evaluation can be seen here.