The HTTP/2 protocol is usually negotiated over the TLS application layer protocol negotiation extension (TLS-ALPN). A persistent HTTP/2 connection can also be made from a HTTP/1.1 request using the `Upgrade` header with the `h2c` value to specify a cleartext communication. The scanner detected that the target is supporting this H2C connection upgrade. If the target application is deployed on a reverse-proxy architecture, attackers could potentially abuse this feature to bypass reverse-proxy access controls or authentication enforcement.