Category:OWASP AntiSamy Project .NET

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What is AntiSamy .NET?

The OWASP AntiSamy .NET 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 gets persisted on the server. The term malicious code in terms of web applications is usually regarded only as 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.

Philosophically, AntiSamy .NET is a departure from all 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. So, we get that.

Unfortunately, that's just not very usable in this situation. Typical Internet users are largely ineffective 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.

Socioeconomically, AntiSamy .NET is a have-not enabler. Private companies like Google, MySpace, eBay, etc. have come up with proprietary solutions for solving this problem. This introduces two problems. One is that proprietary solutions are not usually all that good, and even if they are, well - naturally they're reluctant to share this hard-earned IP for free. Fortunately, we just don't care. We don't see any reason why only these private companies should have this functionality, so we are releasing this for free.

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 .NET is distributed under a BSD license.

Getting 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 its home on Google Code
2. . Choose one of the standard policy files that matches as close to the functionality you need:

• . antisamy-slashdot.xml
• . (more to come in the near future)

1. . Tailor the policy file according to your site's rules
2. . Call the API from the code

Downloading

Installing

Tailoring the policy file

Running

Using AntiSamy is abnormally easy. Here is an example of invoking AntiSamy with a policy file:

       AntiSamy _as = new AntiSamy();
       Policy policy;
       string filename = null;
       filename = Server.MapPath("./properties/antisamy-slashdot.xml");
       policy = Policy.getInstance(filename);
       CleanResults results = _as.scan(txtInput.Text, policy);
       lblOutput.Text = results.getCleanHTML();
       string s = "";
       for (int i = 0; i < results.getErrorMessages().Count; i++)
       {
           s += results.getErrorMessages()[i].ToString() + "<p/>"; 
       }
       lblErrors.Text = s;

Contacting us

OWASP AntiSamy mailing list

Emailing the project lead

=== Issue tracking ===