What is DOM-based cross-site scripting?#
DOM-based cross-site scripting () is a type of attack where an attacker injects malicious code into a website’s Document Object Model (DOM), allowing them to execute arbitrary JavaScript code on the client-side. This type of attack is particularly dangerous because it can be used to steal sensitive user data, take control of user sessions, and perform other malicious actions. According to the OWASP Cheat Sheet Series, DOM-based attacks can be prevented by following guidelines such as escaping untrusted data before inserting it into the DOM and using safe JavaScript functions or properties to populate the DOM.
How service workers work#
Service workers are small scripts that run in the background of a web application, allowing developers to manage network requests, cache resources, and handle offline capabilities. However, service workers can also introduce vulnerabilities if not properly secured. As noted by PortSwigger Research, service workers can be hijacked via DOM clobbering, allowing attackers to execute malicious code on the client-side. This can be achieved by exploiting vulnerabilities in the service worker’s importScripts() function, which can be influenced by query string parameters.
Content Security Policy and worker-src directive#
Content Security Policy (CSP) is a security feature that helps prevent cross-site scripting attacks by defining which sources of content are allowed to be executed within a web page. The worker-src directive is a part of CSP that specifies valid sources for Worker, SharedWorker, or ServiceWorker scripts. According to MDN, the worker-src directive can be used to prevent cross-site scripting attacks by restricting the sources of service worker scripts. For example, a website can set the worker-src directive to only allow service worker scripts from its own domain, preventing attackers from injecting malicious scripts from other domains.
DOM clobbering and its relation to CSP bypass#
DOM clobbering is a technique used by attackers to bypass Content Security Policy (CSP) restrictions by manipulating the DOM to inject malicious code. As explained by PortSwigger Research, DOM clobbering can be used to bypass CSP restrictions by exploiting vulnerabilities in the DOM, allowing attackers to inject malicious code into the DOM. This can be achieved by using techniques such as HTML injection, DOM manipulation, and JavaScript injection.
Comparison of DOM-based and traditional #
| DOM-based | Traditional | |
|---|---|---|
| Attack vector | Injecting malicious code into the DOM | Injecting malicious code into the HTML response |
| Exploitation | Exploits vulnerabilities in the DOM | Exploits vulnerabilities in the server-side code |
| Impact | Can be used to steal sensitive user data, take control of user sessions, and perform other malicious actions | Can be used to steal sensitive user data, take control of user sessions, and perform other malicious actions |
| Prevention | Can be prevented by following guidelines such as escaping untrusted data before inserting it into the DOM and using safe JavaScript functions or properties to populate the DOM | Can be prevented by following guidelines such as validating user input, using prepared statements, and escaping untrusted data before inserting it into the HTML response |
| Bottom line: While both DOM-based and traditional can be used to inject malicious code into a website, they have different attack vectors, exploitation methods, and impacts. |
Detecting DOM-based in service workers#
Detecting DOM-based vulnerabilities in service workers can be challenging, but there are several techniques and tools that can be used. As noted by MDN, the require-trusted-types-for directive can be used to instruct user agents to control the data passed to DOM sink functions, reducing the risk of DOM-based attacks. Additionally, tools such as DOM Invader can be used to detect DOM clobbering vulnerabilities, which can be used to bypass CSP restrictions.
How to remediate DOM-based vulnerabilities#
Remediating DOM-based vulnerabilities in service workers requires a combination of secure coding practices, testing, and validation. The following steps can be taken:
- Validate user input and escape untrusted data before inserting it into the DOM
- Use safe JavaScript functions or properties to populate the DOM
- Implement Content Security Policy (CSP) and set the worker-src directive to restrict the sources of service worker scripts
- Use the require-trusted-types-for directive to instruct user agents to control the data passed to DOM sink functions
- Test and validate the service worker code to ensure it is secure and free of vulnerabilities By following these steps, developers can reduce the risk of DOM-based attacks and protect their users’ sensitive data.
How to detect DOM-based in service workers#
- Step 1: Validate user input and escape untrusted data before inserting it into the DOM.
- Step 2: Use safe JavaScript functions or properties to populate the DOM.
- Step 3: Implement Content Security Policy (CSP) and set the worker-src directive to restrict the sources of service worker scripts.
FAQ#
What is the difference between DOM-based and traditional ?#
DOM-based is a type of attack where an attacker injects malicious code into a website’s Document Object Model (DOM), while traditional is a type of attack where an attacker injects malicious code into the HTML response.
How can I prevent DOM clobbering attacks?#
DOM clobbering attacks can be prevented by implementing Content Security Policy (CSP) and setting the worker-src directive to restrict the sources of service worker scripts.
What tools can I use to detect DOM-based vulnerabilities in service workers?#
Tools such as DOM Invader can be used to detect DOM clobbering vulnerabilities, which can be used to bypass CSP restrictions.