CVE-2026-25150 is a prototype pollution vulnerability identified in the Qwik JavaScript framework, specifically in the formToObj() function within the @builder.io/qwik-city middleware. Qwik is designed for high-performance web applications, and the vulnerable function converts form field names using dot notation (e.g., user.name) into nested JavaScript objects. However, prior to version 1.19.0, this function does not properly sanitize or restrict dangerous property names such as __proto__, constructor, and prototype. Attackers can exploit this by sending specially crafted HTTP POST requests with form fields named to manipulate the Object.prototype, a fundamental JavaScript object from which all objects inherit properties. By polluting Object.prototype, attackers can alter application behavior globally, potentially escalating privileges, bypassing authentication mechanisms, or causing denial of service by corrupting application logic or state. The vulnerability is remotely exploitable without authentication or user interaction, making it highly dangerous. The CVSS v3.1 score of 9.3 reflects the critical nature of this flaw, with network attack vector, low attack complexity, no privileges required, no user interaction, and a scope change that impacts integrity significantly and availability to a lesser extent. Although no public exploits have been reported yet, the widespread use of Qwik in modern web applications means the risk of exploitation is substantial if unpatched. The issue was publicly disclosed and patched in version 1.19.0, and users are strongly advised to upgrade immediately. The vulnerability falls under CWE-1321, which relates to improper control of object prototype attributes, a known vector for severe JavaScript-based attacks.

For European organizations, the impact of this vulnerability can be severe. Many enterprises and service providers use modern JavaScript frameworks like Qwik to build interactive web applications, including e-commerce platforms, financial services portals, and government websites. Exploitation could allow attackers to escalate privileges within the application, bypass authentication controls, or disrupt service availability, leading to data breaches, fraud, or service outages. This is particularly critical for sectors handling sensitive personal data under GDPR, as unauthorized access or data manipulation could result in regulatory penalties and reputational damage. Additionally, denial of service conditions could affect business continuity and customer trust. The vulnerability’s ease of exploitation without authentication increases the risk of automated attacks and widespread scanning. Organizations with public-facing Qwik-based applications are especially vulnerable, and the cross-cutting nature of prototype pollution means that even indirect impacts on downstream services or integrations could occur. The lack of known exploits currently provides a window for proactive mitigation, but the critical severity necessitates urgent action.

To mitigate this vulnerability, European organizations should immediately upgrade all Qwik framework instances to version 1.19.0 or later, where the prototype pollution flaw has been patched. Beyond patching, developers should implement strict input validation and sanitization on all form field names, explicitly disallowing dangerous property names such as __proto__, constructor, and prototype. Web application firewalls (WAFs) can be configured to detect and block suspicious POST requests containing these payloads. Security teams should monitor application logs for anomalous form submissions or unexpected changes in object properties. Conducting code reviews and static analysis focusing on object prototype manipulation can help identify similar risks. Organizations should also consider implementing runtime application self-protection (RASP) solutions to detect and prevent prototype pollution attacks dynamically. Finally, maintaining an inventory of applications using Qwik and integrating vulnerability management processes will ensure timely updates and reduce exposure.