Overview
CVE-2025-66415 describes a route bypass vulnerability found in fastify-reply-from, a Fastify plugin used to forward HTTP requests to other servers. Prior to version 12.5.0, a malicious actor could craft a specific URL that bypassed intended route restrictions. This would allow unauthorized access to routes that should have been protected by the defined reply.from configurations. This issue has been resolved in version 12.5.0 of the plugin.
Technical Details
The vulnerability stems from insufficient validation of the request URL when using reply.from to proxy requests. An attacker could manipulate the URL in a way that circumvents the route matching logic, effectively accessing unintended endpoints on the target server. This could be achieved by carefully crafting the path or query parameters in the request URL.
For example, imagine a scenario where reply.from is configured to forward requests from /api/users to an internal service. An attacker could potentially craft a URL like /api/users/../admin, which, if not properly sanitized, could be interpreted by the backend server as /api/admin, bypassing the intended restriction and granting access to administrative functionalities.
CVSS Analysis
The National Vulnerability Database (NVD) has not yet assigned a CVSS score to this vulnerability. However, given that it allows for route bypass and potential unauthorized access, the potential impact could be significant, depending on the sensitivity of the exposed routes. Further analysis is required to accurately assess its severity.
Possible Impact
Exploitation of this vulnerability could lead to several negative consequences, including:
- Unauthorized Access: Attackers could access restricted routes and functionalities that are not intended for public access.
- Data Breach: Exposure of sensitive data stored on the backend server.
- Privilege Escalation: In some cases, successful exploitation could lead to privilege escalation, granting attackers administrative control over the application.
- Denial of Service (DoS): By exploiting the vulnerability, attackers might be able to disrupt the normal operation of the application.
Mitigation and Patch Steps
The recommended solution is to upgrade to fastify-reply-from version 12.5.0 or later. This version includes a fix that addresses the URL validation issue and prevents route bypass attacks.
To update the plugin, use the following command:
npm install @fastify/reply-from@latestAlternatively, if upgrading is not immediately possible, consider implementing a temporary workaround by adding additional input validation and sanitization to your Fastify routes to prevent malicious URL manipulation.
References
Commit fixing the vulnerability on GitHub
GitHub Security Advisory
