DOM Clobbering via DOMPurify In-Place Sanitization

Executive Summary

DOMPurify is a tool used to sanitize HTML, MathML, and SVG to prevent cross-site scripting (XSS) attacks. The vulnerability in versions prior to 3.4.7 involves a flaw in the IN_PLACE sanitization process.

Specifically, when DOMPurify sanitizes content inside a <template> element, it may skip sanitizing shadow contents attached to elements within <template>.content. This allows attacker-controlled markup, such as malicious event handlers, JavaScript URLs, or scripts, to remain intact after sanitization.

If an application clones and inserts the sanitized template, the malicious markup could execute, leading to potential XSS attacks.

The issue is fixed in DOMPurify version 3.4.7.

Useful 0 Not Useful 0

Detection Guidance

Detecting this vulnerability requires checking if your system or application uses a vulnerable version of DOMPurify (prior to 3.4.7) and if it employs IN_PLACE sanitization on templates containing shadow contents.

• Identify applications using DOMPurify: Search your codebase or dependencies for references to DOMPurify. For example, in a Node.js environment, you can check package.json for the DOMPurify version: grep -r "dompurify" /path/to/project.
• Check DOMPurify version: If DOMPurify is installed, verify its version. In Node.js, you can run: npm list dompurify or check the version in the package-lock.json or yarn.lock file.
• Review code for IN_PLACE sanitization: Search for instances where DOMPurify.sanitize is called with the IN_PLACE option, particularly on templates containing shadow DOM content. Example search: grep -r "DOMPurify.sanitize.*IN_PLACE" /path/to/project.
• Inspect template usage: Look for code that clones or inserts template.content, especially if shadow DOM is involved. Example search: grep -r "template.content" /path/to/project.

There are no network-based detection methods for this vulnerability, as it is a client-side code issue rather than a network-exploitable flaw.

Useful 0 Not Useful 0

Impact Analysis

This vulnerability can impact you in several ways if you are using an affected version of DOMPurify (prior to 3.4.7) in your web application:

• Exposure to cross-site scripting (XSS) attacks: Attackers could inject malicious scripts or event handlers into your application, which may execute when sanitized templates are cloned and inserted.
• Compromise of user data: If an attacker successfully exploits this vulnerability, they could steal sensitive user data, such as session cookies, credentials, or personal information.
• Unauthorized actions: Malicious scripts could perform actions on behalf of users without their consent, such as making unauthorized requests or modifying application data.
• Reputation damage: A successful XSS attack could harm your organization's reputation, leading to loss of user trust and potential legal consequences.

To mitigate these risks, you should update to DOMPurify version 3.4.7 or later.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability can affect compliance with common standards and regulations in the following ways:

• GDPR (General Data Protection Regulation): If this vulnerability leads to unauthorized access or disclosure of personal data, it could violate GDPR requirements for data protection and security. Organizations may face fines or legal action if they fail to protect user data adequately.
• HIPAA (Health Insurance Portability and Accountability Act): For organizations handling protected health information (PHI), this vulnerability could result in unauthorized access to sensitive health data. Non-compliance with HIPAA security rules may lead to penalties and reputational damage.
• PCI DSS (Payment Card Industry Data Security Standard): If your application processes payment card data, an XSS vulnerability could lead to non-compliance with PCI DSS requirements for securing cardholder data. This may result in fines or loss of payment processing capabilities.

To maintain compliance, organizations should address this vulnerability promptly by updating to the fixed version of DOMPurify and ensuring their applications are secure against XSS attacks.

Useful 0 Not Useful 0

Mitigation Strategies

To mitigate this vulnerability, follow these steps:

• Upgrade DOMPurify to version 3.4.7 or later. This version includes the fix for the IN_PLACE sanitization issue with shadow contents in templates.
• If upgrading is not immediately possible, avoid using the IN_PLACE sanitization option on templates containing shadow DOM content. Instead, use standard sanitization methods without IN_PLACE.
• Review and audit your codebase for instances where DOMPurify.sanitize is called with IN_PLACE on templates, and refactor to use safer alternatives if necessary.
• Ensure that any dynamic content inserted into the DOM, especially from untrusted sources, is properly sanitized using the latest version of DOMPurify.

Useful 0 Not Useful 0