To mitigate this issue, you should take the following steps:
Immediate Response: If you haven't already done so, take your website offline temporarily to prevent further damage.
Investigate and Block: Analyze the Sentry error and performance tracking data to understand the nature of the attack and the entry points being used by the attacker.
Input Validation and Sanitization: Ensure that all user inputs are properly validated and sanitized before using them in your application code. Use frameworks or libraries that automatically handle input validation and sanitization to prevent XSS attacks.
Content Security Policy (CSP): Implement a Content Security Policy on your website to limit the sources from which scripts can be loaded. A well-configured CSP can prevent the execution of injected scripts.
Use Safe Libraries: Only use well-maintained and secure third-party libraries. Regularly update them to the latest versions that address security issues.
Prevent Unauthorized Access: Ensure that sensitive parts of your application are protected from unauthorized access.
Error Handling: Properly handle errors and exceptions in your code to avoid leaking sensitive information to potential attackers.
Server-Side Rendering (SSR): If possible, consider using Server-Side Rendering to reduce the risk of XSS attacks.
Regular Security Audits: Conduct regular security audits of your codebase to identify and address any potential security weaknesses.
Report: Report the attack to the appropriate authorities and take legal action if necessary.
Remember, it is essential to address this issue urgently to prevent further damage and protect your users' data and privacy. Security should always be a top priority in web development, and regular security testing and monitoring can help you stay ahead of potential attacks.