dom based cross site scripting prevention

Encode all characters using the \xHH format. Validation becomes more complicated when accepting HTML in user input. In order to mitigate against the CSS url() method, ensure that you are URL encoding the data passed to the CSS url() method. Get started with Burp Suite Professional. Except for alphanumeric characters, encode all characters with the HTML Entity, Except for alphanumeric characters, encode all characters with the, Out of date framework plugins or components, Where URLs are handled in code such as this CSS { background-url : javascript:alert(xss); }. If youre not using a framework or need to cover gaps in the framework then you should use an output encoding library. Cross-site scripting ( XSS) vulnerabilities first became known through the CERT Advisory CA-2000-02 (Malicious HTML Tags Embedded in Client Web Requests), although these vulnerabilities had been exploited before. If a JavaScript library such as jQuery is being used, look out for sinks that can alter DOM elements on the page. So HTML encoding cannot be used to allow the developer to have alternate representations of the tag for example. In an XSS attack, an attacker uses web-pages or web applications to send malicious code and compromise users' interactions with a vulnerable application. Each variable used in the user interface should be passed through an output encoding function. Trusted Types force you to process a value somehow, but don't yet define what the exact processing rules are, and whether they are safe. Ensure JavaScript variables are quoted, JavaScript Hex Encoding, JavaScript Unicode Encoding, Avoid backslash encoding (. DOM based XSS is extremely difficult to mitigate against because of its large attack surface and lack of standardization across browsers. DOM-based XSS simply means a cross-site scripting vulnerability that occurs in the DOM ( Document Object Model) of your site rather than in HTML. The other alternative is using N-levels of encoding. The encoder safe lists can be customized to include Unicode ranges appropriate to the app during startup, in Program.cs: For example, using the default configuration using a Razor HtmlHelper similar to the following: The preceding markup is rendered with Chinese text encoded: To widen the characters treated as safe by the encoder, insert the following line into Program.cs. On the client side, the HTTP response does not change but the script executes in malicious manner. Note that browsers behave differently with regards to URL-encoding, Chrome, Firefox, and Safari will URL-encode location.search and location.hash, while IE11 and Microsoft Edge (pre-Chromium) will not URL-encode these sources. There are several methods and attributes which can be used to directly render HTML content within JavaScript. Login here. 99% of the time it is an indication of bad or lazy programming practice, so simply don't do it instead of trying to sanitize the input. Each variable in a web application needs to be protected. The problem is that if companyName had the value "Johnson & Johnson". DOM-based Cross-site Scripting (DOM XSS) is a particular type of a Cross-site Scripting vulnerability. 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. This cheat sheet provides guidance to prevent XSS vulnerabilities. When URL encoding in DOM be aware of character set issues as the character set in JavaScript DOM is not clearly defined (Mike Samuel). This means you will need to use alternative elements like img or iframe. In this case, AngularJS will execute JavaScript inside double curly braces that can occur directly in HTML or inside attributes. Here are some examples of encoded values for specific characters. DOM-based Cross Site Scripting : DOM XSS stands for Document Object Model-based Cross-site Scripting. Others have a root cause on the client, where the JavaScript code calls dangerous functions with user-controlled content. The defined rules will HTML-escape < characters to prevent the creation of new HTML elements. Therefore, the primary recommendation is to avoid including untrusted data in this context. A list of output encoding libraries is included in the appendix. In other words, add a level of indirection between untrusted input and specified object properties. The payload can be manipulated to deface the target application using a prompt that states: Your session has expired. Now all the violations are reported to //my-csp-endpoint.example, but the website continues to work. Rather, a malicious change in the DOM environment causes client code to run unexpectedly. OWASP are producing framework specific cheatsheets for React, Vue, and Angular. This cushions your application against an XSS attack, and at times, you may be able to prevent it, as well. 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. In DOM-based cross-site scripting, the HTML source code and response of the attack . This would be like a DOM Based XSS attack as it is using rendered JavaScript rather than HTML, however, as it passes though the server it is still classed as reflected or stored XSS depending on where the value is initially set. DOM-based vulnerabilities occur in the content processing stage performed on the client, typically in client-side JavaScript. Level up your hacking and earn more bug bounties. The following is an example vulnerability which occurs in the JavaScript context and HTML subcontext: Let's look at the individual subcontexts of the execution context in turn. Definition DOM Based XSS (or as it is called in some texts, "type-0 XSS") is an XSS attack wherein the attack payload is executed as a result of modifying the DOM "environment" in the victim's browser used by the original client side script, so that the client side code runs in an "unexpected" manner. However, if the pages returned from your web application utilize a content type of text/xhtml or the file type extension of *.xhtml then HTML encoding may not work to mitigate against XSS. Using the right combination of defensive techniques is necessary to prevent XSS. The good news is that if user input is handled properly at the foundation level (e.g. Products Insight Platform Solutions XDR & SIEM INSIGHTIDR Threat Intelligence THREAT COMMAND Vulnerability Management INSIGHTVM Dynamic Application Security Testing INSIGHTAPPSEC The enterprise-enabled dynamic web vulnerability scanner. . To use the configurable encoders via DI your constructors should take an HtmlEncoder, JavaScriptEncoder and UrlEncoder parameter as appropriate. Don't use untrusted input as part of a URL path. HTML Attribute Contexts refer to placing a variable in an HTML attribute value. The appropriate encoding to use in the above case would be only JavaScript encoding to disallow an attacker from closing out the single quotes and in-lining code, or escaping to HTML and opening a new script tag. //The following DOES WORK because the encoded value is a valid variable name or function reference. element.SetAttribute () element [attribute]= However, frameworks aren't perfect and security gaps still exist in popular frameworks like React and Angular. You might already recognize some of them, as browsers vendors and web frameworks already steer you away from using these features for security reasons. Use only safe functions like document.innerText and document.textContent. For details, see the Google Developers Site Policies. This variable includes some characters which are used in XSS attacks, namely <, " and >. Spaces, quotes, punctuation and other unsafe characters will be percent encoded to their hexadecimal value, for example a space character will become %20. At a basic level XSS works by tricking your application into inserting a