CVE-2025-59837: 
JavaScript vulnerability analysis and mitigation

CVE-2025-59837 affects Astro, a web framework, specifically versions 5.13.4 through 5.13.9. The vulnerability is a bypass of a previous security fix (CVE-2025-58179) where the image proxy domain validation can be circumvented using backslashes in the href parameter. This vulnerability was discovered and disclosed on October 28, 2025, and has been patched in version 5.13.10 (GitHub Advisory).

The vulnerability exists in Astro's image proxy functionality where the domain validation mechanism can be bypassed using backslash characters in the href parameter. The issue stems from an incomplete fix for a previous vulnerability (CVE-2025-58179). While the previous fix blocked 'http://', 'https://' and '//' patterns, it failed to account for backslash variants that could be normalized to remote URLs. The vulnerability has been assigned a CVSS v3.1 score of 7.2 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N (GitHub Advisory).

The vulnerability can lead to Server-Side Request Forgery (SSRF) and potentially Cross-Site Scripting (XSS). This allows attackers to make server-side requests to arbitrary URLs, potentially accessing internal resources or executing malicious code (GitHub Advisory).

The vulnerability has been fixed in Astro version 5.13.10. The fix includes improved validation of remote paths by detecting and blocking various backslash patterns, including URL-encoded backslashes and protocol-specific variants. Users should upgrade to version 5.13.10 or later to mitigate this vulnerability (GitHub Commit).