CVE-2025-61925 is a vulnerability classified under CWE-470 (Use of Externally-Controlled Input to Select Classes or Code, also known as Unsafe Reflection) affecting the Astro web framework versions prior to 5.14.2. The core issue arises because Astro reflects the value of the HTTP header X-Forwarded-Host in the output of Astro.url without any validation or sanitization. Typically, web servers like nginx use the Host header to route requests and forward other headers such as X-Forwarded-Host. An attacker can craft a request with mismatched Host and X-Forwarded-Host headers, injecting malicious values into Astro.url output. This can manipulate URLs used in the application, such as canonical links or login/registration URLs, potentially redirecting users to attacker-controlled domains. This redirection can facilitate phishing or credential theft. The risk is amplified in setups where Astro is used in on-demand or dynamic rendering mode behind caching proxies, as maliciously crafted pages can be cached and served to subsequent users, expanding the attack surface beyond the initial attacker. Unlike many other frameworks that implement allowlists or avoid reflecting such headers, Astro lacked this validation prior to version 5.14.2. The vulnerability has a CVSS v3.1 score of 6.5 (medium severity), with network attack vector, low attack complexity, no privileges or user interaction required, impacting integrity and availability but not confidentiality directly. No known exploits are currently reported in the wild. The fix involves proper validation or sanitization of the X-Forwarded-Host header before reflecting it in Astro.url output, as implemented in version 5.14.2.

For European organizations, this vulnerability poses a risk primarily to web applications built using vulnerable versions of the Astro framework (<5.14.2) that rely on dynamic or on-demand rendering and are deployed behind caching proxies such as nginx. The manipulation of URLs can lead to phishing attacks, credential interception, and user redirection to malicious sites, undermining user trust and potentially causing data integrity issues. Cached malicious responses can affect multiple users, increasing the scope of impact. Industries with high web presence such as e-commerce, finance, government portals, and healthcare could be particularly affected due to the sensitivity of user credentials and data. The vulnerability does not directly expose confidential data but can facilitate indirect compromise through social engineering or session hijacking. Availability could also be impacted if attackers exploit the vulnerability to disrupt normal URL routing or cause denial of service via cache poisoning. Given the widespread adoption of Astro in modern web development and the common use of caching proxies in European IT infrastructure, the threat is relevant and should be addressed promptly to avoid reputational damage and regulatory consequences under GDPR if user data is compromised.

European organizations should immediately upgrade all Astro framework instances to version 5.14.2 or later, where the vulnerability is patched. For environments where immediate upgrade is not feasible, implement strict validation and sanitization of the X-Forwarded-Host header at the web server or application gateway level, ensuring only trusted domains are accepted. Configure caching proxies to avoid caching responses that include user-controllable headers or disable caching for dynamic pages that use Astro.url. Employ Content Security Policy (CSP) headers to restrict redirection targets and mitigate the impact of malicious URL injection. Conduct thorough code reviews to identify any usage of Astro.url that could be influenced by headers and refactor to use safer alternatives or explicit allowlists. Monitor web logs for anomalous requests with mismatched Host and X-Forwarded-Host headers. Educate developers on the risks of unsafe reflection and the importance of header validation. Finally, integrate automated security testing in CI/CD pipelines to detect similar header injection issues in future development.