CVE-2025-54793 is an Open Redirect vulnerability (CWE-601) found in the Astro web framework versions 5.2.0 through 5.12.7. Astro is a modern web framework designed for building content-driven websites, supporting server-side rendering (SSR) via Node or Cloudflare adapters. The vulnerability arises from the trailing slash redirection logic when handling URL paths containing double slashes. Specifically, an attacker can craft URLs with double slashes followed by an arbitrary external domain, such as https://mydomain.com//malicious-site.com/, causing the application to redirect users to the attacker-controlled domain. This behavior occurs because the framework incorrectly processes the double slash path segment as a protocol-relative URL, enabling redirection to untrusted external sites. Notably, this issue does not affect static sites or those deployed on Netlify or Vercel, as they do not use the vulnerable SSR adapters. The vulnerability has a CVSS 4.0 base score of 5.5 (medium severity), reflecting its network attack vector, low complexity, and no required privileges or user interaction. While no known exploits are currently reported in the wild, the flaw increases the risk of phishing and social engineering attacks by enabling attackers to lure users to malicious domains under the guise of a trusted site. The issue is fixed in Astro version 5.12.8. As a network-level mitigation, blocking outgoing HTTP redirect responses with a Location header starting with '//' can prevent exploitation by disallowing protocol-relative redirects to external domains.

For European organizations using Astro versions 5.2.0 to 5.12.7 with SSR on Node or Cloudflare, this vulnerability poses a significant risk to user trust and brand reputation. Attackers can exploit the open redirect to craft phishing campaigns that appear to originate from legitimate corporate domains, increasing the likelihood of credential theft, malware delivery, or other social engineering attacks. This is particularly concerning for sectors with high user interaction such as e-commerce, finance, healthcare, and government services. The vulnerability does not directly compromise system confidentiality or integrity but facilitates indirect attacks that can lead to data breaches or fraud. Additionally, organizations relying on Astro for customer-facing portals or internal tools accessible externally may experience increased phishing incidents, potentially leading to regulatory scrutiny under GDPR if personal data is compromised. The lack of required authentication or user interaction lowers the barrier for attackers to exploit this flaw at scale. However, since static sites and deployments on Netlify or Vercel are unaffected, organizations using those deployment models face no risk from this vulnerability.

1. Upgrade all affected Astro instances to version 5.12.8 or later immediately to apply the official patch addressing the open redirect issue. 2. For organizations unable to upgrade promptly, implement network-level controls to block HTTP redirect responses containing Location headers that begin with '//', preventing protocol-relative redirects to external domains. This can be done via web application firewalls (WAFs), reverse proxies, or CDN edge rules. 3. Review and audit all URL redirection logic in custom code or integrations to ensure no similar open redirect patterns exist. 4. Educate users and staff about phishing risks associated with URL redirection vulnerabilities and encourage vigilance when clicking on links, even from trusted domains. 5. Monitor web server logs and security alerts for unusual redirect patterns or spikes in redirect-related traffic that may indicate exploitation attempts. 6. Consider implementing Content Security Policy (CSP) headers to restrict navigation to trusted domains, mitigating the impact of open redirects. 7. For organizations using Cloudflare or Node SSR adapters, verify that the deployment configurations do not override or bypass the patched redirect logic.