For example, a numeric string containing only the characters 0-9 won't trigger an XSS attack. I will show you three examples of DOM-based XSS attacks in this article. All the Acunetix developers come with years of experience in the web security sphere. Scale dynamic scanning. Finally, to fix the problem in our initial code, instead of trying to encode the output correctly which is a hassle and can easily go wrong we would simply use element.textContent to write it in a content like this: It does the same thing but this time it is not vulnerable to DOM based cross-site scripting vulnerabilities. Trusted Types heavily reduce the DOM XSS attack surface of your application. For information on sources and sinks, read the following article: Finding the Source of a DOM-based XSS Vulnerability with Acunetix. 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. Trusted Types give you the tools to write, security review, and maintain applications free of DOM XSS vulnerabilities by making the dangerous web API functions secure by default. The problem is that if companyName had the value "Johnson & Johnson". The web application dynamically generates a web page that contains this untrusted data. A Computer Science portal for geeks. This variable includes some characters which are used in XSS attacks, namely <, " and >. 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); }. Trusted Types are supported in Chrome 83, and a polyfill is available for other browsers. 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. In a reflected DOM XSS vulnerability, the server processes data from the request, and echoes the data into the response. The following are some of the main sinks that can lead to DOM-XSS vulnerabilities: The following jQuery functions are also sinks that can lead to DOM-XSS vulnerabilities: In addition to the general measures described on the DOM-based vulnerabilities page, you should avoid allowing data from any untrusted source to be dynamically written to the HTML document. Limit access to object properties when using object[x] accessors (Mike Samuel). How to Prevent DOM-based Cross-site Scripting - blackMORE Ops The majority of DOM XSS vulnerabilities can be found quickly and reliably using Burp Suite's web vulnerability scanner.

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