The Qwik City framework is vulnerable to a critical prototype pollution flaw that allows unauthenticated attackers to achieve privilege escalation, authentication bypass, or denial of service.

This vulnerability resides in the formToObj() function within the @builder.io/qwik-city middleware. It fails to sanitize sensitive property names like __proto__ during dot-notation processing, allowing unauthenticated attackers to inject malicious properties into the global Object prototype.

A successful exploit poses a severe threat to application integrity and availability. Attackers can bypass security controls to gain unauthorized administrative access or crash the application environment entirely. Given the CVSS score of 9.3, this flaw represents a critical risk to any organization utilizing affected versions of the Qwik framework for production web applications.

Immediate Action: Update the @builder.io/qwik-city package to version 1.19.0 or later immediately to eliminate the insecure processing logic.

Proactive Monitoring: Review application logs for unusual HTTP POST requests containing dot-notation keys or reserved keywords such as __proto__ and constructor.

Compensating Controls: Deploy a Web Application Firewall (WAF) with rules configured to block common prototype pollution payloads in request bodies.

Public Exploit Available: false

The severity of this prototype pollution vulnerability cannot be overstated, as it targets the foundation of the JavaScript runtime environment. IT administrators must prioritize the update to version 1.19.0. Failure to patch may result in complete application takeover or persistent denial of service.