👉 Overview
👀 What ?
DOM XSS (Document Object Model Cross-Site Scripting) is a type of cybersecurity vulnerability that allows an attacker to inject malicious scripts into web pages viewed by other users. It occurs when a web application's client-side scripts write user-provided data to the Document Object Model (DOM). The browser then executes the data written to the DOM with the same trust and permissions as it would legitimate site script.
🧐 Why ?
Understanding DOM XSS is crucial due to its prevalence and potential to cause significant harm. An attacker exploiting a DOM XSS vulnerability can potentially take over user accounts, perform actions on the user's behalf, and access sensitive information. This vulnerability poses a serious threat to web application security, making it a key area of focus for both developers and cybersecurity professionals.
⛏️ How ?
To detect DOM XSS vulnerabilities, one can use static analysis tools that scan JavaScript code for dangerous patterns, or dynamic analysis tools that execute the code in a controlled environment and observe the results. Mitigation strategies include validating and sanitizing user inputs, implementing Content Security Policies (CSP), and keeping all client-side code as simple as possible to minimize the attack surface.
⏳ When ?
DOM XSS vulnerabilities have been a concern since the early 2000s with the growing use of JavaScript in web development. Despite its long history, cases of DOM XSS are still being discovered in modern web applications.
⚙️ Technical Explanations
At a technical level, DOM XSS involves the execution of malicious scripts due to unsafe handling of user input within client-side JavaScript code. The Document Object Model is a programming interface for HTML and XML documents. It provides a structured representation of the document and defines a way that the structure can be manipulated by scripts, leading to changes in the document's structure, style, or content. A DOM XSS attack occurs when an application writes user-controlled input to the DOM without proper sanitization, allowing for the execution of malicious scripts. These scripts can then interact with the web page and perform actions with the same permissions as the user, leading to potential information disclosure, session theft, or even remote code execution.