In these scenarios, you should do URL encoding, followed by HTML attribute encoding. You should apply HTML attribute encoding to variables being placed in most HTML attributes. Avoid treating untrusted data as code or markup within JavaScript code. Any variable that does not go through this process is a potential weakness. Otherwise, again, your security efforts are void. Fewer XSS bugs appear in applications built with modern web frameworks. A script within the later response contains a sink which then processes the data in an unsafe way. There are two ways to do this. What is WordPress Cross-site Scripting (XSS) and How to prevent it? Scale dynamic scanning. This cheat sheet provides guidance to prevent XSS vulnerabilities. What is XSS? Impact, Types, and Prevention - Bright Security DOM-based XSS Vulnerability - All you need to know - Crashtest Security //any code passed into lName is now executable. Generally, attributes that accept JavaScript, such as onClick, are NOT safe to use with untrusted attribute values. It allows an attacker to circumvent the same origin policy, which is designed to segregate different websites from each other. With Trusted Types enabled, the browser accepts a TrustedHTML object for sinks that expect HTML snippets. This cheatsheet is a list of techniques to prevent or limit the impact of XSS. There are a variety of sinks that are relevant to DOM-based vulnerabilities. If you use the default encoders then any you applied to character ranges to be treated as safe won't take effect - the default encoders use the safest encoding rules possible. It uses the Document Object Model (DOM), which is a standard way to represent HTML objects in a hierarchical manner. How to Prevent Cross Site Scripting | XSS Attack Prevention Note that the browser's "View source" option won't work for DOM XSS testing because it doesn't take account of changes that have been performed in the HTML by JavaScript. Read the entire Acunetix Web Application Vulnerability Report. For more details on how to prevent DOM-based XSS attacks, you can read the OWASP DOM-based XSS Prevention Cheat Sheet. Ideally, the correct way to apply encoding and avoid the problem stated above is to server-side encode for the output context where data is introduced into the application. Already got an account? This cheatsheet addresses DOM (Document Object Model) based XSS and is an extension (and assumes comprehension of) the XSS Prevention Cheatsheet. To prevent server-side XSS, don't generate HTML by concatenating strings and use safe contextual-autoescaping templating libraries instead. Now that you know more about cross-site scripting attacks and their impact, let's take a look at how you can prevent cross-site scripting or XSS attacks. Before putting untrusted data into JavaScript place the data in an HTML element whose contents you retrieve at runtime. Here are some examples of how they are used: One option is utilize ECMAScript 5 immutable properties in the JavaScript library. Directly setting event handler attributes will allow JavaScript encoding to mitigate against DOM based XSS. Encode all characters using the \xHH format. In order to mitigate against the CSS url() method, ensure that you are URL encoding the data passed to the CSS url() method. Event handlers such as onload and onerror can be used in conjunction with these elements. See how our software enables the world to secure the web. DOM-based Cross-site Scripting (DOM XSS) is a particular type of a Cross-site Scripting vulnerability. Here are the proper security techniques to use to prevent XSS attacks: Sanitize outputs properly. DOM-based attack Reflected XSS Attacks The simplest type of XSS attack is where the application immediately processes and returns unsanitized user input in a search result, error message, or other HTTP responses. Please refer to the list below for details. Markdown, coupled with a parser that strips embedded HTML, is a safer option for accepting rich input. Cross-site scripting (also known as XSS) is a web security vulnerability that allows an attacker to compromise the interactions that users have with a vulnerable application. This variable includes some characters which are used in XSS attacks, namely <, " and >. Dangerous attributes include any attribute that is a command execution context, such as onclick or onblur. How to Prevent DOM-based Cross-site Scripting - blackMORE Ops Then client-side encode (using a JavaScript encoding library such as node-esapi) for the individual subcontext (DOM methods) which untrusted data is passed to. At a basic level XSS works by tricking your application into inserting a