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xss

Sanitize untrusted HTML (to prevent XSS) with a configuration specified by a Whitelist

Sanitize untrusted HTML (to prevent XSS) with a configuration specified by a Whitelist.


xss is a module used to filter input from users to prevent XSS attacks. (What is XSS attack?)

Project Homepage: http://jsxss.com

Try Online: http://jsxss.com/en/try.html

中文版文档


  • Specifies HTML tags and their attributes allowed with whitelist
  • Handle any tags or attributes using custom function.
  • the xss module: 8.2 MB/s
  • xss() function from module validator@0.3.7: 4.4 MB/s

For test code please refer to benchmark directory.

$ npm install xss
$ bower install xss

Or

$ bower install https://github.com/leizongmin/js-xss.git
var xss = require('xss');
var html = xss('<script>alert("xss");</script>');
console.log(html);

Shim mode (reference file test/test.html):

<script src="https://raw.github.com/leizongmin/js-xss/master/dist/xss.js"></script>
<script>
// apply function filterXSS in the same way
var html = filterXSS('<script>alert("xss");</scr' + 'ipt>');
alert(html);
</script> 

AMD mode - shim:

<script>
require.config({
  baseUrl: './',
  paths: {
    xss: 'https://raw.github.com/leizongmin/js-xss/master/dist/xss.js'
  },
  shim: {
    xss: {exports: 'filterXSS'}
  }
})
require(['xss'], function (xss) {
  var html = xss('<script>alert("xss");</scr' + 'ipt>');
  alert(html);
});
</script> 

You can use the xss command line tool to process a file. Usage:

xss -i <input_file> -o <output_file>

Example:

$ xss -i origin.html -o target.html

Run the following command, them you can type HTML code in the command-line, and check the filtered output:

$ xss -t

For more details, please run $ xss -h to see it.

When using the xss() function, the second parameter could be used to specify custom rules:

options = {};  // Custom rules 
html = xss('<script>alert("xss");</script>', options);

To avoid passing options every time, you can also do it in a faster way by creating a FilterXSS instance:

options = {};  // Custom rules 
myxss = new xss.FilterXSS(options);
// then apply myxss.process() 
html = myxss.process('<script>alert("xss");</script>');

Details of parameters in options would be described below.

By specifying a whiteList, e.g. { 'tagName': [ 'attr-1', 'attr-2' ] }. Tags and attributes not in the whitelist would be filter out. For example:

// only tag a and its attributes href, title, target are allowed 
var options = {
  whiteList: {
    a: ['href', 'title', 'target']
  }
};
// With the configuration specified above, the following HTML: 
// <a href="#" onclick="hello()"><i>Hello</i></a> 
// would become: 
// <a href="#">Hello</a> 

For the default whitelist, please refer xss.whiteList.

By specifying the handler function with onTag:

function onTag (tag, html, options) {
  // tag is the name of current tag, e.g. 'a' for tag <a> 
  // html is the HTML of this tag, e.g. '<a>' for tag <a> 
  // options is some addition informations: 
  //   isWhite    boolean, whether the tag is in whitelist 
  //   isClosing  boolean, whether the tag is a closing tag, e.g. true for </a> 
  //   position        integer, the position of the tag in output result 
  //   sourcePosition  integer, the position of the tag in input HTML source 
  // If a string is returned, the current tag would be replaced with the string 
  // If return nothing, the default measure would be taken: 
  //   If in whitelist: filter attributes using onTagAttr, as described below 
  //   If not in whitelist: handle by onIgnoreTag, as described below 
}

By specifying the handler function with onTagAttr:

function onTagAttr (tag, name, value, isWhiteAttr) {
  // tag is the name of current tag, e.g. 'a' for tag <a> 
  // name is the name of current attribute, e.g. 'href' for href="#" 
  // isWhiteAttr whether the tag is in whitelist 
  // If a string is returned, the attribute would be replaced with the string 
  // If return nothing, the default measure would be taken: 
  //   If in whitelist: filter the value using safeAttrValue as described below 
  //   If not in whitelist: handle by onIgnoreTagAttr, as described below 
}

By specifying the handler function with onIgnoreTag:

function onIgnoreTag (tag, html, options) {
  // Parameters are the same with onTag 
  // If a string is returned, the tag would be replaced with the string 
  // If return nothing, the default measure would be taken (specifies using 
  // escape, as described below) 
}

By specifying the handler function with onIgnoreTagAttr:

function onIgnoreTagAttr (tag, name, value, isWhiteAttr) {
  // Parameters are the same with onTagAttr 
  // If a string is returned, the value would be replaced with this string 
  // If return nothing, then keep default (remove the attribute) 
}

By specifying the handler function with escapeHtml. Following is the default function (Modification is not recommended):

function escapeHtml (html) {
  return html.replace(/</g, '&lt;').replace(/>/g, '&gt;');
}

By specifying the handler function with safeAttrValue:

function safeAttrValue (tag, name, value) {
  // Parameters are the same with onTagAttr (without options) 
  // Return the value as a string 
}

If you allow the attribute style, the value will be processed by cssfilter module. The cssfilter module includes a default css whitelist. You can specify the options for cssfilter module like this:

myxss = new xss.FilterXSS({
  css: {
    whiteList: {
      position: /^fixed|relative$/,
      top: true,
      left: true,
    }
  }
});
html = myxss.process('<script>alert("xss");</script>');

If you don't want to filter out the style content, just specify false to the css option:

myxss = new xss.FilterXSS({
  css: false,
});

For more help, please see https://github.com/leizongmin/js-css-filter

By using stripIgnoreTag parameter:

  • true filter out tags not in the whitelist
  • false: by default: escape the tag using configured escape function

Example:

If stripIgnoreTag = true is set, the following code:

code:<script>alert(/xss/);</script> 

would output filtered:

code:alert(/xss/);

By using stripIgnoreTagBody parameter:

  • false|null|undefined by default: do nothing
  • '*'|true: filter out all tags not in the whitelist
  • ['tag1', 'tag2']: filter out only specified tags not in the whitelist

Example:

If stripIgnoreTagBody = ['script'] is set, the following code:

code:<script>alert(/xss/);</script> 

would output filtered:

code:

By using allowCommentTag parameter:

  • true: do nothing
  • false by default: filter out HTML comments

Example:

If allowCommentTag = false is set, the following code:

code:<!-- something --> END

would output filtered:

code: END
var source = '<div a="1" b="2" data-a="3" data-b="4">hello</div>';
var html = xss(source, {
  onIgnoreTagAttr: function (tag, name, value, isWhiteAttr) {
    if (name.substr(0, 5) === 'data-') {
      // escape its value using built-in escapeAttrValue function 
      return name + '="' + xss.escapeAttrValue(value) + '"';
    }
  }
});
 
console.log('%s\nconvert to:\n%s', source, html);

Result:

<div a="1" b="2" data-a="3" data-b="4">hello</div>
convert to:
<div data-a="3" data-b="4">hello</div>
var source = '<x><x-1>he<x-2 checked></x-2>wwww</x-1><a>';
var html = xss(source, {
  onIgnoreTag: function (tag, html, options) {
    if (tag.substr(0, 2) === 'x-') {
      // do not filter its attributes 
      return html;
    }
  }
});
 
console.log('%s\nconvert to:\n%s', source, html);

Result:

<x><x-1>he<x-2 checked></x-2>wwww</x-1><a>
convert to:
&lt;x&gt;<x-1>he<x-2 checked></x-2>wwww</x-1><a>
var source = '<img src="img1">a<img src="img2">b<img src="img3">c<img src="img4">d';
var list = [];
var html = xss(source, {
  onTagAttr: function (tag, name, value, isWhiteAttr) {
    if (tag === 'img' && name === 'src') {
      // Use the built-in friendlyAttrValue function to escape attribute 
      // values. It supports converting entity tags such as &lt; to printable 
      // characters such as < 
      list.push(xss.friendlyAttrValue(value));
    }
    // Return nothing, means keep the default handling measure 
  }
});
 
console.log('image list:\n%s', list.join(''));

Result:

image list:
img1, img2, img3, img4
var source = '<strong>hello</strong><script>alert(/xss/);</script>end';
var html = xss(source, {
  whiteList:          [],        // empty, means filter out all tags 
  stripIgnoreTag:     true,      // filter out all HTML not in the whilelist 
  stripIgnoreTagBody: ['script'] // the script tag is a special case, we need 
                                 // to filter out its content 
});
 
console.log('text: %s', html);

Result:

text: helloend
Copyright (c) 2012-2016 Zongmin Lei(雷宗民) <leizongmin@gmail.com>
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