Steeltoe vulnerable to management-port isolation bypass via spoofed Host header

Summary

When Steeltoe management endpoints are configured to listen on an alternate port (Management:Endpoints:Port is configured), the middleware responsible for restricting access to the endpoints uses the Host HTTP header rather than the actual network socket port.

Impact

An unauthenticated remote attacker can reach every actuator endpoint using a specially crafted HTTP request.

Affected configuration

• The application's public port is accessible over from the network.
• Management:Endpoints:Port is configured to a value different from the application's main listener port.
• The request scheme matches Management:Endpoints:SslEnabled. For example, http when SslEnabled is false (the default), or https when SslEnabled is true.

Mitigations

If an immediate upgrade to a patched version is not possible:

• Add explicit ASP.NET Core authorization (RequireAuthorization) to all sensitive actuator endpoints as a defense-in-depth measure independent of port isolation.
• Configure the reverse proxy or load balancer to enforce the Host header value and prevent clients from setting an arbitrary port.