CVE-2026-25148 is a Cross-Site Scripting (XSS) vulnerability identified in the Qwik JavaScript framework, specifically affecting versions prior to 1.19.0. Qwik is designed for high-performance web applications and uses server-side rendering (SSR) to improve load times and SEO. The vulnerability stems from improper neutralization of input during the serialization of virtual attributes in the SSR process. Virtual attributes are custom attributes used internally by Qwik to manage component state and behavior. An attacker can craft malicious input that, when processed by the vulnerable Qwik SSR engine, is embedded unsafely into the generated HTML output. This allows injection of arbitrary JavaScript code that executes in the context of the victim’s browser when they visit the affected web page. The CVSS 4.0 vector indicates the attack is network-based (AV:N), requires low attack complexity (AC:L), no privileges (PR:N), no user interaction (UI:P), and no confidentiality, integrity, or availability impact beyond the script execution (VC:N, VI:N, VA:N). The scope is limited (S:L), meaning the vulnerability affects only the vulnerable component and does not extend to other components. While no known exploits have been reported, the vulnerability poses a risk of session hijacking, credential theft, phishing, or other malicious actions if exploited. The issue was patched in Qwik version 1.19.0, which properly sanitizes or encodes virtual attribute inputs during SSR to prevent script injection. Organizations using Qwik for web applications should prioritize upgrading to this version. Additionally, reviewing custom code that manipulates virtual attributes or SSR output is advised to ensure no unsafe patterns remain. Implementing Content Security Policy (CSP) headers can further mitigate the impact by restricting script execution sources.

For European organizations, this vulnerability can lead to client-side script injection attacks, compromising user sessions, stealing sensitive data, or performing unauthorized actions on behalf of users. Web applications built with vulnerable Qwik versions expose their users to these risks, potentially damaging reputation and violating data protection regulations such as GDPR if personal data is compromised. The impact is particularly significant for organizations with customer-facing web portals, e-commerce platforms, or internal tools accessed via browsers. Attackers exploiting this vulnerability could bypass same-origin policies, leading to cross-site request forgery (CSRF), credential theft, or distribution of malware. The medium severity reflects that while the vulnerability does not directly compromise server-side systems, the client-side impact can cascade into broader security incidents. European organizations with high web traffic and reliance on modern JavaScript frameworks are at increased risk, especially if patching is delayed. Furthermore, regulatory scrutiny in Europe mandates prompt remediation of vulnerabilities that could expose personal data, increasing the operational and compliance risks associated with this flaw.

1. Upgrade all Qwik framework instances to version 1.19.0 or later immediately to apply the official patch that neutralizes the vulnerability. 2. Audit server-side rendering code and any custom handling of virtual attributes to ensure proper input validation and encoding practices are followed, preventing injection of unsafe content. 3. Implement strict Content Security Policy (CSP) headers to restrict the execution of inline scripts and limit script sources, reducing the impact of any potential XSS payloads. 4. Conduct thorough security testing, including automated and manual penetration testing focused on SSR and attribute serialization components, to detect residual injection risks. 5. Educate developers on secure coding practices related to SSR and attribute handling in JavaScript frameworks to prevent similar vulnerabilities in custom code. 6. Monitor web application logs and user reports for signs of exploitation attempts or unusual script execution behaviors. 7. If immediate upgrade is not feasible, consider temporary mitigations such as disabling features that rely on virtual attributes or sanitizing inputs at the application layer before they reach the framework. 8. Maintain an incident response plan to quickly address any detected exploitation and notify affected users if personal data exposure occurs.