It was my understanding that when you have an Stunnel Server configured with 'verify=2', that the client that connects must have a certificate signed by the same CA/SubCA combination that the server does. So for example:

  - My_Root_Ca (private CA)

    - Some_Random_Cert.pem

    - Stunnel_Sub_Ca:

      - Server.pem

      - Client.pem

    - Postgres_Sub_Ca:

      - Server.pem

      - postgres_user.pem

With the above structure in place (and the stunnel server using Stunnel_Sub_Ca/Server.pem) if someone tried to connect in with the Stunnel_Sub_Ca/Client.pem cert, it would work... but if they tried to connect in with Postgres_Sub_Ca/Server.pem, it wouldn't.

Unfortunately we're not seeing that behavior... we're seeing a behavior where *every* cert signed by the overall Root CA is validated. We're able to connect in using Some_Random_Cert.pem, Postgres_Sub_Ca/Server.pem and Postgres_Sub_Ca/postgres_user.pem.

This feels wrong ... what am I missing?

(We're using Stunnel 4.55 btw)

Matt Wise

Sr. Systems Architect

Nextdoor.com