Exploiting Drag-and-Drop XSS via Invisible Iframes in ING ES

Cross-Site Scripting (XSS) remains a persistent threat to web applications, despite advancements in security practices. One often overlooked attack vector involves drag-and-drop functionality, particularly when combined with auto-executing JavaScript inputs and invisible iframes. This article details a potential drag-and-drop XSS vulnerability in ING ES (Spain), focusing on the technical aspects of its exploitation.

Understanding the Vulnerability:

The core issue stems from the combination of three factors:

1. Drag-and-Drop Functionality: ING ES, like many modern web applications, allows users to drag and drop files or content into certain input fields or areas.
2. Auto-Executing JavaScript Inputs: Certain input fields, intended for specific functionalities, may automatically execute JavaScript code embedded within the dragged content. This often occurs when the application attempts to parse and display the dragged content, potentially without proper sanitization.
3. Invisible Iframes: An attacker can create an invisible iframe that contains malicious JavaScript. By dragging this iframe into the vulnerable input field, the embedded JavaScript can be executed within the context of the ING ES domain.

Proof of concept:

Hosting the Malicious HTML:

The attacker hosts the HTML file on a server they control.

Dragging and Dropping:

The attacker, or a victim tricked into doing so, drags the URL of the hosted HTML file into the vulnerable input field on the ING ES website. Alternatively, the attacker could create a link to the hosted html file, and the victim could drag the link into the vulnerable input.

JavaScript Execution:

When the ING ES application attempts to process the dragged content, the invisible iframe is rendered, and the embedded JavaScript payload is executed within the browser’s context. Because the javascript is executed within the context of the ING ES domain, the attacker can steal cookies, session tokens, or manipulate the DOM.

Mitigation Strategies:

To prevent drag-and-drop XSS vulnerabilities, ING ES should implement the following security measures:

1. Input Sanitization: Thoroughly sanitize all user-supplied input, including data received through drag-and-drop operations. Employ strict input validation and encoding to prevent the execution of malicious JavaScript.

2. Content Security Policy (CSP): Implement a robust CSP to restrict the execution of inline JavaScript and external scripts. This will significantly reduce the impact of XSS attacks.

3. Iframe Restrictions: Restrict the use of iframes or implement strict sandboxing for iframes to prevent them from executing malicious code.
   Consider disallowing drag and drop of iframes.

4. Regular Security Audits: Conduct regular security audits and penetration testing to identify and address potential vulnerabilities.
   Specifically test drag-and-drop functionalities with various payloads.

5. User Education: Educate users about the risks of drag-and-drop attacks and encourage them to be cautious when interacting with untrusted content.

Responsible Disclosure:

If such a vulnerability is discovered, it is crucial to follow responsible disclosure practices. Report the vulnerability to ING ES security team through their appropriate channels, allowing them to address the issue before public disclosure.

Conclusion:

Drag-and-drop XSS vulnerabilities, while often subtle, can pose a significant threat to web applications. By understanding the techniques used in these attacks and implementing appropriate mitigation strategies, organizations like ING ES can strengthen their security posture and protect their users from harm.