There are valid use cases for TLS middleboxes. Anyone having to secure a networks outbound access to only essential services has run into the “I have to allow all of AWS/GCP/Azure/CloudFlare/…” for some critical tool to work.
Options are:
- Allow all out (nope, not secure)
- Allow all to the cloud providers IP range (still terrible)
- Filter on SNI but don’t inspect the payload (better than no security, and doesn’t require plaintext access).
- Full MITM TLS proxy (performance bottleneck, and now we have plaintext access to all your data, which we really don’t want and didn’t previously require to do the filtering).
- Try convince the third party service to run on a handful of static IPs that aren’t behind a global load balancer with access to the rest of the cloud providers customer domains. (Yeah right)
See: Hospitals. Payment Networks. IoT networks.