Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability exists in a web framework component used for building applications and APIs, potentially allowing unauthenticated access to protected functions. This issue arises from a discrepancy in how encoded slashes are handled between the framework's routing and its middleware layer, enabling attackers to bypass security controls on parameterized paths. The main concern is confirming relevance and exposure within your Fastify-based services.
- Attackers can bypass access controls.
- It affects security layers like authentication.
- Confirm if your Fastify applications are affected.
Attack Path
How an attacker could exploit the issue
An attacker can bypass security controls by sending a specially crafted URL. This happens because the middleware and the framework's router interpret encoded slashes in different ways, allowing an attacker to reach a protected route handler that the middleware fails to block. This bypass does not require authentication or any special setup.
- Entry Condition: Attacker can send network requests.
- Trigger Point: Crafted URL bypasses middleware path matching.
- Resulting Risk: Unauthorized access to protected handlers.
Live Threat
Current exploitation, exposure, and threat context
This vulnerability could allow an attacker to bypass security middleware, such as authentication or authorization checks, on parameterized URL paths. This bypass could be achieved by sending a specially crafted URL that includes an encoded slash, which the middleware and the router interpret differently. When middleware is used for critical security decisions on these paths, an attacker could potentially access protected routes without proper credentials or authorization.
- Protected route handlers.
- Encoded slashes in URLs bypass middleware.
- Unauthorized access to sensitive routes.
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability impacts applications using `@fastify/middie` for middleware, particularly when handling authentication, authorization, or rate limiting on parameterized paths. Application owners and platform teams are likely responsible for remediation. The first practical step involves identifying all instances of the affected middleware, determining their reachability and criticality, and then coordinating the upgrade or implementing workarounds based on the assessed risk.
- Application owners should own the issue.
- Verify middleware usage on parameterized paths.
- Coordinate @fastify/middie upgrade.
