For example if you want to use user input to write in a div tag element don't use innerHtml, instead use innerText or textContent. This can be done via a function such as: All the Acunetix developers come with years of experience in the web security sphere. You must regularly patch DOMPurify or other HTML Sanitization libraries that you use. 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. For many years DOM XSS has been one of the most prevalentand dangerousweb security vulnerabilities. . Rather, a malicious change in the DOM environment causes client code to run unexpectedly. 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. Since then, it has extended to include injection of basically any content, but we still refer to this as XSS. You can remove the offending code, use a library, create a Trusted Type policy or, as a last resort, create a default policy. document.CreateTextNode () and append it in the appropriate DOM location. For example: Modern web applications are typically built using a number of third-party libraries and frameworks, which often provide additional functions and capabilities for developers. Using the wrong encoding method may introduce weaknesses or harm the functionality of your application. We are looking for web developers to participate in user research, product testing, discussion groups and more. Variables should not be interpreted as code instead of text. In order to add a variable to a HTML context safely, use HTML entity encoding for that variable as you add it to a web template. Sometimes users need to author HTML. Websites may also store data on the server and reflect it elsewhere. This is a Safe Sink and will automatically URL encode data in it. There are numerous methods which implicitly eval() data passed to it that must be avoided. Use untrusted data on only the right side of an expression, especially data that looks like code and may be passed to the application (e.g., location and eval()). There are two distinct groups of cross-site scripting. Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted websites. DOM-based cross-site scripting (DOM XSS) is a web vulnerability, a subtype of cross-site scripting. Before putting untrusted data into JavaScript place the data in an HTML element whose contents you retrieve at runtime. For example, the general rule is to HTML Attribute encode untrusted data (data from the database, HTTP request, user, back-end system, etc.) XSS is one of the most common and dangerous web vulnerabilities, and it is . How to prevent DOM-based cross-site scripting? For example, a JavaScript encoded string will execute even though it is JavaScript encoded. There will be situations where you use a URL in different contexts. Consider adopting the following controls in addition to the above. Don't mutate DOM directly. For details, see the Google Developers Site Policies. Limit access to object properties when using object[x] accessors (Mike Samuel). It uses the Document Object Model (DOM), which is a standard way to represent HTML objects in a hierarchical manner. There are two ways to do this. The best way to fix DOM based cross-site scripting is to use the right output method (sink). In order to understand DOM based XSS, one needs to see the fundamental difference between Reflected and Stored XSS when compared to DOM based XSS. This enables attackers to execute malicious JavaScript, which typically allows them to hijack other users' accounts. Acunetix developers and tech agents regularly contribute to the blog. URL Contexts refer to variables placed into a URL. If your web site makes heavy use of non-Latin characters, such as Chinese, Cyrillic or others this is probably not the behavior you want. If your data gets URL-encoded before being processed, then an XSS attack is unlikely to work. After the page's JavaScript applies this malicious URL to the back link's href, clicking on the back link will execute it: Another potential sink to look out for is jQuery's $() selector function, which can be used to inject malicious objects into the DOM. \u0064\u006f\u0063\u0075\u006d\u0065\u006e\u0074, \u0077\u0072\u0069\u0074\u0065\u006c\u006e, "\u0048\u0065\u006c\u006c\u006f\u0020\u0057\u006f\u0072\u006c\u0064", "\u0061\u006c\u0065\u0072\u0074\u0028\u0031\u0031\u0029", "url(<%=ESAPI.encoder().encodeForJavascript(ESAPI.encoder().encodeForURL(companyName))%>)", '<%=ESAPI.encoder().encodeForJavascript(ESAPI.encoder().encodeForURL(userRelativePath))%>', "<%= Encode.forJavaScript(untrustedData) %>", "<%=ESAPI.encoder().encodeForJavascript(untrustedData)%>", "customFunction('<%=doubleJavaScriptEncodedData%>', y)", //HTML encoding is happening in JavaScript, "javascript:myFunction('<%=untrustedData%>', 'test');", "javascript:myFunction('<%=ESAPI.encoder().encodeForJavascript(ESAPI.encoder().encodeForURL(untrustedData)) %>', 'test');",