CVE-2025-64764: 
JavaScript vulnerability analysis and mitigation

A high severity vulnerability (CVE-2025-64764) was discovered in Astro's server islands feature, affecting versions <= 5.15.6. The vulnerability allows for reflected XSS attacks through the server islands feature, regardless of component template intentions. The issue was patched in version 5.15.8 and was published on November 19, 2025 (GitHub Advisory).

The vulnerability exists in the server islands feature which runs in an isolated context outside of the page request using the path pattern '/_server-islands/[name]'. The issue stems from the ability to inject slots containing XSS payloads by manipulating the 'e' parameter with a value of 'file', which returns the absolute path of the island file. This path is then used as a tag name, allowing for code injection regardless of the component template's intended functionality. The vulnerability has a CVSS score of 7.1 (High) with a vector string of CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N (GitHub Advisory).

The vulnerability allows attackers to execute arbitrary JavaScript code in the context of the victim's browser through reflected XSS attacks. This can lead to theft of sensitive information, session hijacking, and other client-side attacks. The CVSS metrics indicate low impact on confidentiality but high impact on integrity, with no impact on availability (GitHub Advisory).

Users should upgrade to Astro version 5.15.8 or later which contains the patch for this vulnerability (GitHub Advisory).