Those are Safe Sinks as long as the attribute name is hardcoded and innocuous, like id or class. setAttribute and methods because they will automatically HTML Attribute Encode. If you're writing to a HTML Attribute with JavaScript, look at the. Quoting also significantly reduces the characterset that you need to encode, making your application more reliable and the encoding easier to implement. Quoting makes it difficult to change the context a variable operates in, which helps prevent XSS. It’s critical to use quotation marks like " or ' to surround your variables. “HTML Context” refers to inserting a variable between two basic HTML tags like a or. Using the wrong encoding method may introduce weaknesses or harm the functionality of your application. There are many different output encoding methods because browsers parse HTML, JS, URLs, and CSS differently. A list of output encoding libraries is included in the appendix. ![]() ![]() Each variable used in the user interface should be passed through an output encoding function. If you’re not using a framework or need to cover gaps in the framework then you should use an output encoding library. Automatic encoding and escaping functions are built into most frameworks. This section covers each form of output encoding, where to use it, and when you should not use dynamic variables at all.įirst, when you wish to display data as the user typed it in, start with your framework’s default output encoding protection. Variables should not be interpreted as code instead of text. When you need to safely display data exactly as a user types it in, output encoding is recommended. Output encoding and HTML sanitization help address those gaps. However, no framework is perfect and security gaps still exist in popular frameworks like React and Angular. Frameworks make it easy to ensure variables are correctly validated and escaped or sanitised. Any variable that does not go through this process is a potential weakness. Ensuring that all variables go through validation and are then escaped or sanitized is known as perfect injection resistance. Thus, all variables in a web application needs to be protected. In order for an XSS attack to be successful, an attacker must be able to to insert and execute malicious content in a webpage. OWASP will be producing framework specific cheatsheets for React, Vue, and Angular. There will be times where you need to do something outside the protection provided by your framework, which means that Output Encoding and HTML Sanitization can be critical. When you use a modern web framework, you need to know how your framework prevents XSS and where it has gaps. Out of date framework plugins or components.Angular’s bypassSecurityTrustAs* functions.React cannot handle javascript: or data: URLs without specialized validation.React’s dangerouslySetInnerHTML without sanitising the HTML.escape hatches that frameworks use to directly manipulate the DOM. ![]() However, developers need to know that problems can occur if frameworks are used insecurely, such as: Framework Security ¶įortunately, applications built with modern web frameworks have fewer XSS bugs, because these frameworks steer developers towards good security practices and help mitigate XSS by using templating, auto-escaping, and more. Since no single technique will solve XSS, using the right combination of defensive techniques will be necessary to prevent XSS. This cheatsheet contains techniques to prevent or limit the impact of XSS. XSS attacks are serious and can lead to account impersonation, observing user behaviour, loading external content, stealing sensitive data, and more. ![]() Since then, the term has widened to include injection of basically any content. Originally this term was derived from from early versions of the attack that were primarily focused on stealing data cross-site. This cheat sheet helps developers prevent XSS vulnerabilities.Ĭross-Site Scripting (XSS) is a misnomer. Insecure Direct Object Reference PreventionĬross Site Scripting Prevention Cheat Sheet ¶ Introduction ¶ Output Encoding for “JavaScript Contexts” Output Encoding for “HTML Attribute Contexts”
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