Secondly, avoid serialization which could be vulnerable to injection attacks that execute code in the serialization process. JavaScript runtime environments, like the browser and the server-side Node. A practical example of this is the following:. With this, a programmer is trying to create a dynamic way to access data on the DOM. In this example, the assumption is that getElementform is also potentially user controlled, as well as the elementId variable.
There are better ways of performing this task without the need for eval , so you should avoid dynamic code like this by all means. On the Node. In this example, the general assumption is that the exact file we want to require is dynamic, and potentially user-controlled, in which again we have potential code injection security vulnerabilities.
The maintainers of dustjs did their best to escape potentially dangerous user input that could flow into insecure code constructs like the eval function, however the escapeHtml function itself had a security flaw, in which it only checked for string types and then escaped the input, where-as it should have also checked for other types, like say, arrays.
This pull request fixed the code injection security vulnerability :. If you use dustjs, you might also introduce the npm package dustjs-helpers to get additional template helpers like math operations and logical operations.
One of those additional helpers is an if condition, which you may end up using like this in your own dust template files:. The problem is that uncontrolled user input in that query parameter device flows directly into the if condition helper, which uses eval, as you can see in line , to evaluate the condition dynamically:. Now everything becomes clear, and shows how several security issues come together in an unforeseen way:.
Do you want to see how I exploited this vulnerability and hacked a real live working application just based on this exact vulnerability? Check it out:. To wrap up the best practice of avoiding eval , I also want to call out other functions which, as a JavaScript developer, you have most certainly heard about or used at least once in your application: setTimeout and setInterval.
A little less known fact about these functions, is that they also receive code strings. For example, it can be used as follows:. Another language construct, similar to the above eval , setTimeout and setInterval is the Function constructor, which allows dynamically to define a function based on string literals.
If you followed closely this far, you already are aware of the potential security issues that could arise from user input flowing into such a function…. Serialization is quite a thing in the Java ecosystem. Notice how the text appears right on the page:. On old Internet Explorer versions, it will set it to 0 to disable it. You can also optionally configure a report URI, though the flag is specific to Chrome-based browsers. This option will report the violation to the specified URI:.
This solution does help in protecting yourself from one type of JS Injection, thereby assuring protection of your website users and their data privacy. Please share your comments below and follow this blog if you are interested in getting more information on JavaScript. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Check out out our contact Page for more details.
Skip to content. JS Injection JavaScript is one of the most popular technologies and is being widely used for web pages and web applications. This option will report the violation to the specified URI: app. The following example shows vulnerable code using the document.
This input will add an image tag to the page that will execute arbitrary JavaScript code inserted by the malicious user in the HTML context. Watch Star.
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