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 to build performant websites and applications, and the vulnerability specifically arises when the server islands feature is utilized. Server islands allow partial hydration of components on the client side, improving performance but introducing complexity in how user input is handled. The vulnerability occurs because the framework improperly neutralizes script-related HTML tags in the generated web pages, allowing attackers to inject malicious JavaScript code via crafted URLs or input parameters that are reflected back in the response. This reflected XSS does not require authentication but does require user interaction, such as clicking a malicious link. The CVSS score of 7.1 (high) reflects the network attack vector, low attack complexity, no privileges required, but user interaction needed, with impacts on confidentiality (data theft) and integrity (session manipulation), though availability is unaffected. No known exploits are reported in the wild yet, but the vulnerability poses a significant risk to applications using vulnerable versions of Astro with server islands enabled. The issue was addressed and patched in version 5.15.8 by improving input sanitization and output encoding to prevent script injection. Organizations using Astro in their web stacks should prioritize upgrading and auditing their use of server islands to mitigate this risk.

For European organizations, the impact of CVE-2025-64764 can be substantial, especially for those operating public-facing web applications built with Astro versions prior to 5.15.8. Successful exploitation can lead to theft of sensitive user data such as authentication tokens, personal information, or financial details, compromising user privacy and trust. Attackers can also manipulate session data or perform actions on behalf of users, leading to potential account takeover or unauthorized transactions. While availability is not directly impacted, the reputational damage and potential regulatory consequences under GDPR for data breaches can be significant. Industries such as e-commerce, finance, healthcare, and government services that rely on Astro for their web presence are particularly at risk. The requirement for user interaction means phishing or social engineering campaigns could be used to lure victims. The lack of known exploits in the wild suggests a window of opportunity for proactive mitigation before widespread attacks occur.

1. Upgrade all Astro framework instances to version 5.15.8 or later immediately to apply the official patch that fixes the XSS vulnerability. 2. Conduct a thorough audit of all web applications using Astro, focusing on those employing the server islands feature, to identify any instances of reflected user input in responses. 3. Implement additional input validation and output encoding layers at the application level to sanitize user-supplied data, especially in URL parameters and form inputs. 4. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 5. Educate development teams on secure coding practices related to client-side rendering and hydration features to prevent similar issues. 6. Monitor web traffic and logs for unusual patterns indicative of attempted XSS exploitation, such as suspicious query strings or script injection attempts. 7. Inform users and stakeholders about the vulnerability and encourage caution with unsolicited links until mitigations are in place. 8. Consider implementing Web Application Firewalls (WAF) with rules targeting reflected XSS patterns as an additional protective measure.