anti

v0.1.7

Published

2 years ago

Anti is an XSS protection module.

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anti xss protection security cross-site scripting clean purge sanitize sanitization DOMParser

Anti

Anti is an Cross-site Scripting (XSS) protection module for the Browser & NodeJS. It uses DOMParser (or NodeJS equivalent XMLDom) rather than Regular expressions (RegEx) to process DOM just as a browser would. This makes Anti safe to many XSS workarounds by nature.

Installation

npm install anti

Usage

You can use Anti in a browser or in NodeJS, pass it an unsanitized string of DOM and get a sanitized string (or a DOM object) in return. Note that the returned String/DOMObject will be wrapped around a div with class="anti".

var XSSParser = new Anti();
var result = XSSParser.parse('<div class="hello world">!</div><script>alert("xss")</script>');
console.log(result);
// Output: <div class="anti"><div class="hello world">!</div></div>

> Browsers

Anti includes full support for browsers. It does not use Regular Expressions (RegEx) but rather the browser's internal method DOMParser. Support for this method is approximately 97% of all browsers (http://caniuse.com/#feat=xml-serializer) and provides superior security compared to innerHTML method. You can include anti.js or anti.min.js from the build folder like so:

...
<body>
...
<script src="build/anti.min.js"></script>
</body>

Or using Browserify

// Install (refer to installation)
var Anti = require('anti');
// Refer to Usage

Alternatively when using Bower

bower install anti
// Include bower_components/anti/build/anti.min.js

Filters

You can modify default filter lists that are extended to every instance of Anti. Filters are an array of lowercase strings that are compared for parsing. If an element tag is a part of the filter it will be kept in the final results. (e.g. script tag is not part of the ACCEPTABLE_BLOCK_ELEMENTS). Instance Filters are as follows:

ACCEPTABLE_BLOCK_ELEMENTS all acceptable DOM elements (e.g. div, table, nav, etc.)
ACCEPTABLE_SANITARY_ATTRIBUTES all acceptable DOM attributes which do not include a URL (e.g. title, height, align, etc.)
ACCEPTABLE_UNSANITARY_ATTRIBUTES all acceptable DOM attributes which include a URL (e.g. href, src, style, etc.)

As Filters are JS arrays you can modify them using Push, Pop, Shift, Unshift methods or you can modify them entirely to your liking:

var XSSParser = new Anti();
// Only allow div, span tags <div>, <span>
XSSParser.ACCEPTABLE_BLOCK_ELEMENTS = ['div', 'span'];

// Only allow title attribute <div title="test">
XSSParser.ACCEPTABLE_SANITARY_ATTRIBUTES = ['title'];
XSSParser.ACCEPTABLE_UNSANITARY_ATTRIBUTES = [];

var result = XSSParser.parse('<div title="test" style="display:none">Hello World!</div><section>This will be excluded</section>');
console.log(result);
// Output: <div class="anti"><div title="test">Hello World!</div></div>

Options

You can pass options while creating an Anti instance or by modifying the Options attribute in that specific instance. e.g.

// Forces Anti to return a DOM object instead of a serialized string, hence you will be able to directly append the output
var options = { serialize: false };

var XSSParser = new Anti(options);
// Alternatively XSSParses.Options.serialize = false
var result = XSSParser.parse('<div>test</div>');
console.log(result);
// Output: [object HTMLDivElement]

Options include:

serialize: Boolean(default: true) Returns a serialized/string DOM instead of a DOM Object
wrapper: String(default: "") A single wrapper element that wraps around the output
experimentalInlineCSS: Boolean(default: false) Allows for inline style parsing and filtering (!EXPERIMENTAL)

Experimental -> Inline CSS Parser

To use experimental feature you'll need to include either anti.experimental.js or anti.experimental.min.js from the build folder. Note that experimental features are available by default in the NodeJS version. Inline CSS feature brings in a built in CSS parser and Url Validator. This feature allows for filtering of inline CSS styles (e.g. style="font-size: 2px; color: red;"). You can enable this feature by passing { experimentalInlineCSS: true } options to the Anti constructor. Note that this method uses an internal parsing function with only one RegEx test to test for validity of url() values. The filter for this method is defined as ACCEPTABLE_CSS_PROPERTIES.

Disclaimer:

This module utilizes a doze of insanity and a drop of blood from the Black Witch of the North to bring joy to your divs and html elements without the hassle of unwanted magic spells and bacteria incorporated with your non-sanitary method of sanitization. Thus it is highly experimental to the extent that even this sentence is currently being tested in our non-existent laboratory which I will assure you is experimental itself. Use it at your own risk.

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