CVE-2025-64525 affects the Astro web framework, specifically versions from 2.16.0 up to but excluding 5.15.5, which implement on-demand rendering. The vulnerability stems from the unsafe handling of the HTTP headers 'x-forwarded-proto' and 'x-forwarded-port'. These headers are typically used to convey the original protocol and port of a client request when passing through proxies or load balancers. Astro uses these headers to construct URLs without proper sanitization or validation, allowing an attacker to manipulate them to influence URL generation. This manipulation enables several attack vectors: (1) Middleware-based protected route bypass via 'x-forwarded-proto', allowing unauthorized access to routes that should be restricted; (2) Denial of Service (DoS) through cache poisoning when a CDN is present, by injecting malicious or misleading cache keys; (3) SSRF attacks by forcing the server to make unintended requests to internal or external resources; (4) URL pollution that can lead to stored cross-site scripting (SXSS) if combined with CDN caching; and (5) Web Application Firewall (WAF) bypass by crafting requests that evade detection mechanisms relying on URL patterns. The vulnerability does not require authentication or user interaction, increasing its risk profile. The CVSS 3.1 score is 6.5, reflecting medium severity with network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, but integrity and availability impacts present. The issue was publicly disclosed on November 13, 2025, and fixed in Astro version 5.15.5. No known exploits have been observed in the wild to date.

For European organizations, the impact of CVE-2025-64525 can be significant, especially for those deploying web applications using vulnerable versions of Astro. Middleware-protected route bypass can lead to unauthorized access to sensitive application areas, potentially exposing confidential business logic or user data. SSRF vulnerabilities can be leveraged to access internal network resources, potentially leading to further compromise or data exfiltration. Cache poisoning attacks can degrade service availability and performance, impacting user experience and trust. URL pollution and potential SXSS can facilitate persistent client-side attacks, harming end users and damaging organizational reputation. Organizations relying on CDNs or WAFs for security may find these defenses circumvented, increasing exposure. Given the widespread adoption of Astro in modern web development, especially among startups and digital service providers in Europe, the threat could affect sectors such as finance, e-commerce, and government services. The medium severity rating indicates a moderate but actionable risk that requires timely remediation to prevent exploitation.

European organizations should immediately assess their use of the Astro framework and identify any deployments running versions >= 2.16.0 and < 5.15.5. The primary mitigation is to upgrade to Astro version 5.15.5 or later, which contains the patch for this vulnerability. Until upgrades are applied, organizations should implement strict validation and sanitization of the 'x-forwarded-proto' and 'x-forwarded-port' headers at the application or proxy level to prevent malicious manipulation. Configuring CDNs and caching layers to ignore or properly validate these headers can reduce cache poisoning risks. Web Application Firewalls should be updated with custom rules to detect and block suspicious header values or unusual URL patterns associated with this vulnerability. Additionally, review middleware logic to ensure it does not rely solely on these headers for access control decisions. Conduct thorough security testing, including SSRF and cache poisoning scenarios, to validate mitigations. Monitoring logs for anomalous header values and unusual internal requests can help detect exploitation attempts. Finally, educate development teams about secure header handling and the risks of trusting client-supplied headers.