Astro is a modern web framework that includes an image proxy feature designed to fetch and serve images from external URLs. In versions 5.13.4 through 5.13.9, the domain validation mechanism intended to restrict which URLs the proxy can access is flawed. Specifically, the validation can be bypassed by inserting backslash characters within the href parameter, which the proxy fails to properly normalize or sanitize. This allows an attacker to craft URLs that appear safe but actually direct the server to make requests to arbitrary internal or external endpoints. This Server-Side Request Forgery (SSRF) vulnerability (CWE-918) enables attackers to force the server to interact with internal systems, potentially exposing sensitive data or enabling further attacks. Additionally, the vulnerability may facilitate cross-site scripting (CWE-79) if the attacker can inject malicious scripts via the proxy response. The root cause is an incomplete remediation of a prior SSRF vulnerability (CVE-2025-58179), indicating insufficient input validation and normalization. The vulnerability requires no privileges or user interaction, making it highly exploitable remotely. The vendor addressed the issue in version 5.13.10 by improving domain validation and input sanitization to correctly handle backslashes and prevent bypasses. No known exploits are reported in the wild yet, but the high CVSS score of 7.2 reflects the significant risk posed by this vulnerability in web-facing applications.

For European organizations, this SSRF vulnerability poses a considerable risk to confidentiality and integrity. Exploitation could allow attackers to access internal services that are otherwise protected by network segmentation or firewalls, such as internal APIs, metadata services, or databases. This could lead to data leakage, unauthorized actions within internal systems, or pivoting deeper into the network. The potential XSS impact could enable session hijacking or further client-side attacks if malicious scripts are injected and executed in users' browsers. Organizations relying on Astro for web applications, especially those exposing image proxy functionality, may face increased risk of data breaches, service disruption, or reputational damage. Given the ease of exploitation without authentication or user interaction, attackers can automate scanning and exploitation attempts. The impact is amplified in sectors with sensitive data such as finance, healthcare, and government services prevalent in Europe. Additionally, compliance with GDPR and other data protection regulations could be jeopardized if personal data is exposed through this vulnerability.

The primary mitigation is to upgrade all affected Astro instances to version 5.13.10 or later, where the vulnerability is fixed. Organizations should audit their web applications to identify any use of the Astro image proxy and ensure it is not exposed unnecessarily. Implement strict input validation and normalization on all URL parameters, especially those controlling proxy requests, to prevent bypass techniques such as backslash insertion. Employ network-level controls to restrict outbound requests from web servers to only trusted destinations, limiting the potential impact of SSRF. Monitor logs for unusual proxy request patterns or requests to internal IP ranges. Consider deploying Web Application Firewalls (WAFs) with rules targeting SSRF attack patterns. Conduct security testing focusing on SSRF and input validation in web proxies. Finally, educate developers on secure coding practices related to URL handling and proxy usage to prevent similar issues in the future.