CVE-2025-59837 is a Server-Side Request Forgery (SSRF) vulnerability found in the Astro web framework, specifically in its image proxy feature. Astro versions from 5.13.4 up to but not including 5.13.10 contain a flaw where the domain validation mechanism can be bypassed by inserting backslashes in the href parameter. This bypass allows attackers to craft URLs that the server will fetch, potentially accessing internal or restricted network resources. SSRF vulnerabilities are dangerous because they can be used to pivot into internal systems, access sensitive data, or perform unauthorized actions on behalf of the server. Additionally, this vulnerability may lead to cross-site scripting (XSS) attacks due to improper handling of the fetched content. The root cause is an incomplete fix of a previous SSRF vulnerability (CVE-2025-58179), indicating that the validation logic did not fully sanitize or normalize input URLs. The vulnerability requires no privileges or user interaction, making it easier to exploit remotely. The issue was publicly disclosed on October 28, 2025, with a CVSS 3.1 base score of 7.2, indicating high severity. The fix was implemented in Astro version 5.13.10, which properly addresses the domain validation bypass. No known exploits are currently reported in the wild, but the potential impact is significant given the nature of SSRF and XSS combined.

For European organizations, this vulnerability poses a significant risk, especially for those deploying web applications using the Astro framework versions 5.13.4 to 5.13.9. SSRF can allow attackers to access internal services that are not exposed externally, potentially leading to data leakage, unauthorized internal network scanning, or exploitation of other internal vulnerabilities. The possible XSS impact can facilitate session hijacking, phishing, or further compromise of user accounts. Organizations with sensitive internal APIs, cloud metadata services, or private databases accessible from the vulnerable server are at heightened risk. The lack of required authentication or user interaction lowers the barrier for attackers, increasing the likelihood of exploitation. This can disrupt service integrity and confidentiality, damaging organizational reputation and compliance posture under regulations like GDPR. The vulnerability could also be leveraged in multi-stage attacks targeting critical infrastructure or supply chains within Europe.

The primary mitigation is to upgrade all affected Astro framework instances to version 5.13.10 or later, where the vulnerability is fully patched. Organizations should audit their web applications to identify usage of the Astro image proxy and validate that no legacy versions remain in production or staging environments. Implement strict input validation and URL normalization on any user-supplied parameters related to URL fetching. Employ network segmentation and firewall rules to restrict server outbound requests to only trusted domains and services, limiting the impact of any SSRF attempts. Monitor logs for unusual outbound requests or anomalies in image proxy usage patterns. Consider deploying Web Application Firewalls (WAFs) with rules targeting SSRF attack signatures. Conduct security reviews and penetration tests focusing on SSRF and XSS vectors in affected applications. Finally, educate developers about secure coding practices related to URL handling and proxy services.