CVE-2025-64764 is a reflected Cross-Site Scripting (XSS) vulnerability classified under CWE-80, affecting the Astro web framework versions prior to 5.15.8. Astro is a modern web framework used for building performant websites, and the vulnerability specifically manifests when the server islands feature is enabled. Server islands allow partial hydration of components on the client side, improving performance but introducing complexity in input handling. The vulnerability occurs because the framework improperly neutralizes script-related HTML tags in reflected input, allowing attackers to inject malicious JavaScript code that executes in the context of the victim's browser. This reflected XSS does not require authentication but does require user interaction, such as clicking a crafted link. The impact includes potential theft of sensitive information like cookies or session tokens, manipulation of page content, and execution of arbitrary scripts, compromising confidentiality and integrity. Availability is not directly affected. The vulnerability has been addressed in Astro version 5.15.8, which includes proper sanitization and encoding of user input in the server islands feature. No known exploits are reported in the wild as of the publication date, but the high CVSS score (7.1) indicates a significant risk if left unpatched.

For European organizations, this vulnerability poses a significant risk to web applications built with vulnerable versions of Astro, especially those leveraging the server islands feature. Exploitation could lead to unauthorized disclosure of sensitive user data, session hijacking, and potential defacement or manipulation of web content, undermining user trust and compliance with data protection regulations such as GDPR. Industries relying heavily on web presence and user interaction, including e-commerce, finance, healthcare, and government services, could face reputational damage and legal consequences if exploited. The reflected nature of the XSS means attackers can craft malicious URLs to target users, increasing the attack surface. Given the widespread adoption of modern JavaScript frameworks in Europe, the threat is relevant to many organizations, particularly those that have not promptly updated their dependencies or audited their use of server islands. The lack of known exploits in the wild reduces immediate risk but should not lead to complacency.

1. Upgrade all Astro framework instances to version 5.15.8 or later immediately to apply the official patch addressing this vulnerability. 2. Conduct a thorough audit of web applications using Astro to identify usage of the server islands feature and ensure that all user inputs are properly sanitized and encoded before rendering. 3. Implement Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 4. Educate developers on secure coding practices related to input validation and output encoding, especially when using advanced framework features like server islands. 5. Monitor web application logs and user reports for suspicious activity that may indicate attempted exploitation. 6. Employ web application firewalls (WAFs) with updated rules to detect and block reflected XSS attack patterns targeting Astro-based applications. 7. Integrate automated security testing in the CI/CD pipeline to detect XSS vulnerabilities early in the development lifecycle.