CVE-2025-54793 is an Open Redirect vulnerability (CWE-601) affecting the Astro web framework versions 5.2.0 through 5.12.7. Astro is a modern framework used 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, if an attacker crafts a URL with a double slash followed by an external domain (e.g., https://mydomain.com//malicious-site.com/), the application improperly redirects users to the external, potentially malicious domain. This flaw does not affect static site deployments or those hosted on Netlify or Vercel, as these platforms do not utilize the vulnerable SSR adapters. The vulnerability has a CVSS 4.0 base score of 5.5 (medium severity), reflecting its network exploitable nature without requiring authentication or user interaction. The impact primarily involves enabling phishing and social engineering attacks by leveraging trusted domains to redirect users to malicious sites. No known exploits are currently reported in the wild. The issue is resolved in Astro version 5.12.8. As a network-level mitigation, blocking HTTP redirect responses with Location headers starting with double slashes (//) can prevent exploitation.

For European organizations using Astro with SSR on Node or Cloudflare adapters, this vulnerability poses a risk of facilitating phishing and social engineering attacks. Attackers can exploit the open redirect to craft URLs that appear to originate from legitimate, trusted domains, increasing the likelihood of users being deceived into visiting malicious sites. This can lead to credential theft, malware infections, or further compromise of enterprise systems. The vulnerability does not directly compromise system confidentiality, integrity, or availability but serves as an enabler for downstream attacks. Organizations relying on Astro for customer-facing websites or internal portals may see reputational damage and user trust erosion if exploited. Given the medium severity and ease of exploitation without authentication, the threat is significant, especially for sectors with high user interaction such as e-commerce, finance, and public services in Europe.

1. Upgrade all affected Astro instances to version 5.12.8 or later immediately to apply the official fix. 2. For environments where immediate upgrade is not feasible, implement network-level controls to block HTTP redirect responses containing Location headers that start with double slashes (//), as these indicate the malicious redirect pattern. 3. Review and sanitize URL handling logic in custom middleware or routing configurations to ensure no unintended redirects to external domains occur. 4. Employ web application firewalls (WAFs) with rules to detect and block open redirect attempts based on suspicious Location header patterns. 5. Educate users and administrators about the risks of phishing via trusted domains and encourage vigilance when clicking on URLs, especially those with unusual path structures. 6. Monitor web server logs for unusual redirect patterns or spikes in 3xx responses with suspicious Location headers to detect potential exploitation attempts early.