In an attribute name In a tag name Directly in CSS ``` You should also not extend the sanitizer to whitelist the following tags: `script, style, noscript`. In order to prevent additional attacks, this library should only be used if the following requirements are met: UTF-8 character set, JavaScript environment (NodeJS or Browser), and modern browsers (IE11, Edge, Safari, Chrome, Firefox, Opera, iOS Safari, and Mobile Chrome). For more information about inserting the sanitized string safely, see this article: https://www.owasp.org/index.php/XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet. ## Table of Contents - [Why `js-xss`?](#why-js-xss) - [Installation](#installation) - [Usage](#usage) - [Issues](#issues) - [Versioning](#versioning) - [Contributing](#contributing) - [License](#license) - [Dependencies](#dependencies) ### Why [`js-xss`](https://github.com/leizongmin/js-xss)? [js-xss](https://github.com/leizongmin/js-xss) is lightweight (5.5k gzipped) library with an [MIT](https://github.com/leizongmin/js-xss#license) license. It is also highly customizable and works well in both Node.js applications and in the browser. ### Installation Using npm: ```sh npm install --save @esri/arcgis-html-sanitizer ``` Using Yarn: ```sh yarn add @esri/arcgis-html-sanitizer ``` ### Usage #### Import ES Modules ```js import { Sanitizer } from "@esri/arcgis-html-sanitizer"; ``` CommonJS ```js const Sanitizer = require("@esri/arcgis-html-sanitizer").Sanitizer; ``` AMD (Use UMD version in ./dist/umd folder) ```js define(['path/to/dist/umd/arcgis-html-sanitizer'], function(Sanitizer) { ... }) ``` Load as script tag ```html ``` #### Basic Usage ```js // Instantiate a new Sanitizer object const sanitizer = new Sanitizer(); // Sanitize a string const sanitizedHtml = sanitizer.sanitize( '

' ); // sanitizedHtml =>

// Check if a string contains invalid HTML const validation = sanitizer.validate( '

' ); // validation => { // isValid: false // sanitized: '

' // } ``` #### Sanitize JSON In addition to sanitizing strings, this utility also allows you to sanitize full JSON objects. This can be useful if you want to sanitize all the app data returned from the server before using it in your application. If the value passed does not contain a valid JSON data type (String, Number, JSON Object, Array, Boolean, or null), the value will be nullified. **WARNING**: You should never concatenate strings from multiple values in the JSON. Strings values may be safe and pass the sanitizer when separated but become dangerous after they are concatenated. This is intended as a convenience method only. You should run the strings through the sanitizer again after they have been concatenated. ```js // Instantiate a new Sanitizer object const sanitizer = new Sanitizer(); // Deeply sanitize a JSON object const sanitizedJSON = sanitizer.sanitize({ sample: ['

'] }); // sanitizedJSON => { // "sample": ["

"] // } ``` #### Sanitize URLs The ability to sanitize URL strings has been specifically broken out to a public method, `sanitizeUrl`. This can be very useful if you want to sanitize URLs according to the built-in rules, yet you don't want to necessarily extend the whitelist and implement custom filtering options to force sanitization of specific tag attributes. ```js // Instantiate a new Sanitizer object const sanitizer = new Sanitizer(); // Sanitize a URL with a valid protocol const supportedProtocol = sanitizer.sanitizeUrl( "https://example.com/about/index.html" ); // supportedProtocol => "https://example.com/about/index.html" // Sanitize a URL with an invalid protocol const unsupportedProtocol = sanitizer.sanitizeUrl( "smb://example.com/path/to/file.html" ); // unsupportedProtocol => "" ``` #### Sanitize HTML Attribute Values To prevent against XSS, untrusted data going into HTML attribute values need to be [sanitized](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#rule-2-attribute-encode-before-inserting-untrusted-data-into-html-common-attributes), including [`style` attribute values](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#rule-4-css-encode-and-strictly-validate-before-inserting-untrusted-data-into-html-style-property-values). The ability to sanitize HTML attribute values has been specifically broken out to a public method, `sanitizeHTMLAttribute`, specifying the tagname, attribute name, and value. ```js // Instantiate a new Sanitizer object const sanitizer = new Sanitizer(); // Sanitize a safe alt attribute value const unquotedAttribute = sanitizer.sanitizeHTMLAttribute('img', 'alt', 'A picture'); // unquotedAttribute => "A picture" // Sanitize an unsafe alt attribute value const quotedAttribute = sanitizer.sanitizeHTMLAttribute('img', 'alt', '"A picture"'); // quotedAttribute => ""A picture"" // Sanitize unsafe style attribute value const styles = sanitizer.sanitizeHTMLAttribute( 'div', 'style', 'background-image:url("javascript:alert(\"xss\")")' ); // styles => "" ``` Optionally, a custom filter for style attributes can be provided as the final argument, which will be used in place of the default js-xss style attribute filter. ```js const styles = sanitizer.sanitizeHTMLAttribute('div', 'style', 'color:red;', { process: (value: string) => value.indexOf('color') !== -1 ? '' : value /* or additional filtering here */ }); // styles => "" ``` #### Encode HTML The `encodeHTML` method encodes a well-defined set of characters within an HTML string to their hexadecimal HTML entity codes to ensure safe display of the string to the end user. This encodes HTML tags for display as text within an HTML page, it does not sanitize the string to prevent XSS. If you are looking to sanitize, use the `sanitize` method instead. * `&` → `8` * `<` → `<` * `>` → `>` * `"` → `"` * `'` → `'` * `/` → `/` ```js const sanitizer = new Sanitizer(); const input = `a link`; sanitizer.encodeHTML(input); // => "<a href="javascript:alert(document.cookies)">a link</a>" ``` #### Encode Attribute Values The `encodeAttrValue` method encodes all non-alphanumeric ASCII characters to their hexadecimal HTML entity code to ensure safe use as an HTML attribute. This method only encodes characters. It does not directly sanitize the string to remove XSS. If you are looking to sanitize your string, use the `sanitizeHTMLAttribute` method instead. ```js const sanitizer = new Sanitizer(); const input = "javascript:alert(document.cookies)"; sanitizer.encodeAttrValue(input); // => "javascript:alert(document.cookie)" ``` #### Customizing Filter Options Override the default XSS filter options by passing a valid js-xss options object as the first parameter of the constructor. Options available here: https://github.com/leizongmin/js-xss#custom-filter-rules. You can also extend the default options instead of overriding them by passing `true` as the second parameter of the constructor. When extending the filter options `whiteList`, the attribute arrays will automatically be concatenated to the defaults instead of replacing them. ```js const customSanitizer = new Sanitizer({ whiteList: { a: ['data-example'] }, escapeHtml: function () { ... } }, true /* extend defaults */); ``` If you override the built-in filtering using custom filter rules, know that you are taking full control of that particular filtering method. To do this safely, you can pass anything you don't want to handle specifically on to the `js-xss` filtering method. In this example, we want to strip any `href` for the domain `www.mydomain.tld` and pass along everything else to the `js-xss` `safeAttrValue` method. ```js import xss from "xss"; const customSanitizer = new Sanitizer({ safeAttrValue: function(tag, name, value, cssFilter) { // strip anchor href attributes that point to www.mydomain.tld on any protocol, // and allow any other href attributes if (tag === "a" && name === "href") { if (value.indexOf("//www.mydomain.tld") > -1) { return ""; } else { return xss.escapeAttrValue(value); } } // pass everything else onto the `js-xss` `safeAttrValue` method return xss.safeAttrValue(tag, name, value, cssFilter); } }); ``` ### Issues If something isn't working the way you expected, please take a look at [previously logged issues](https://github.com/Esri/arcgis-html-sanitizer/issues) first. Have you found a new bug? Want to request a new feature? We'd [**love**](https://github.com/Esri/arcgis-html-sanitizer/issues/new) to hear from you. ### Versioning For transparency into the release cycle and in striving to maintain backward compatibility, @esri/arcgis-html-sanitizer is maintained under Semantic Versioning guidelines and will adhere to these rules whenever possible. For more information on SemVer, please visit . ### Contributing Esri welcomes contributions from anyone and everyone. Please see our [guidelines for contributing](https://github.com/esri/contributing). #### Developer Instructions Install Dependencies ```sh yarn install ``` Test ```sh yarn test ``` Test in development ```sh yarn run test --watch ``` Build compiled output: - CommonJS Module outputs to `dist/node/index.js`. - ES Module outputs to `dist/esm/index.js` and `dist/esm/index.min.js`. - UMD Module outputs to `dist/umd/arcgis-html-sanitizer.js` and `dist/umd/arcgis-html-sanitizer.min.js`. ```sh yarn build ``` Lint and fix errors ```sh yarn run lint:fix ``` ### License Copyright 2021 Esri Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at > http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. A copy of the license is available in the repository's [LICENSE](./LICENSE) file. ### Dependencies - [js-xss](https://github.com/leizongmin/js-xss) ([MIT](https://github.com/leizongmin/js-xss#license))