Secure XSS Filters ================= *Just sufficient* output filtering to prevent XSS! [![npm version][npm-badge]][npm] [![dependency status][dep-badge]][dep-status] [![Build Status](https://travis-ci.org/yahoo/xss-filters.svg?branch=master)](https://travis-ci.org/yahoo/xss-filters) [npm]: https://www.npmjs.org/package/xss-filters [npm-badge]: https://img.shields.io/npm/v/xss-filters.svg?style=flat-square [dep-status]: https://david-dm.org/yahoo/xss-filters [dep-badge]: https://img.shields.io/david/yahoo/xss-filters.svg?style=flat-square ## Goals - **More Secure.** Context-dependent output filters that are developer-friendly. It is safe to apply these filters like so: `document.write("" + xssFilters.uriInHTMLData(url) + "");` In this example, the traditional wisdom of blindly escaping some special html entity characters (`&` `<` `>` `'` `"` `` ` ``) would not stop XSS (e.g., when `url` is equal to `javascript:alert(1)` or ` onclick=alert(1)`). - **Faster with Just Sufficient Encoding.** Encode the *minimal* set of characters to thwart JavaScript executions, thus preventing XSS attacks while keeping most characters intact. Compared to the traditional blindly escape filter, our filters are [up to two times faster](http://jsperf.com/context-sensitive-vs-blindly-escape), and there is no more double-encoding problems such as '&lt;'!! ![alt Visualizing the concept of just sufficient encoding](https://ierg4210.github.io/web/images/xss-filters/xss-filters.png) Figure 1. "Just sufficient" encoding based on the HTML5 spec. ## Design - **Automation.** Nothing can be better than applying context-sensitive output escaping automatically. Integration with Handlebars template engine is now available. Check out [express-secure-handlebars](https://www.npmjs.com/package/express-secure-handlebars) for server-side use, or [secure-handlebars](https://www.npmjs.com/package/secure-handlebars) for client-side use. - **Standards Compliant.** The XSS filters are designed primarily based on the modern [HTML 5 Specification](https://html.spec.whatwg.org/multipage/syntax.html#syntax). The principle is to escape characters specific to each non-scriptable output context. Hence, untrusted inputs, once sanitized by context-sensitive escaping, cannot break out from the containing context. This approach stops malicious inputs from being executed as scripts, and also prevents the age-old problem of over/double-encoding. - **Carefully Designed.** Every filter is heavily scrutinized by Yahoo Security Engineers. The specific sets of characters that require encoding are minimized to preserve usability to the greatest extent possible. ## Quick Start ### Server-side (nodejs) Install the [xss-filters npm](https://www.npmjs.com/package/xss-filters), and include it as a dependency for your project. ```sh npm install xss-filters --save ``` Require *xss-filters*, and you may use it with your favorite template engine. Or just use it directly: ```javascript var express = require('express'); var app = express(); var xssFilters = require('xss-filters'); app.get('/', function(req, res){ var firstname = req.query.firstname; //an untrusted input collected from user res.send('

Hello, ' + xssFilters.inHTMLData(firstname) + '!

'); }); app.listen(3000); ``` ### Client-side (browser) Simply download the latest minified version from the [`dist/`](./dist) folder OR from the CDN. Embed it in your HTML file, and all filters are available in a global object called `xssFilters`. ```html ... ``` API Documentations ------- ### WARNINGS (1) Filters **MUST ONLY** be applied to UTF-8-encoded documents. (2) **DON'T** apply any filters inside any scriptable contexts, i.e., `

	Stars	Issues	Version	Updated	Created
express-sanitizer	45	5	1.0.6	3 years ago	10 years ago
validator.js	255	15	2.0.4	4 years ago	11 years ago
xss-escape			0.0.6	9 years ago	10 years ago
xss-filters	1,074	7	1.2.7	8 years ago	9 years ago

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