It happened on several occasions that buggy filters modify or remove headers critical to Envoy's internals (or other filters in the chain). Envoy should check if required request or response headers are still present and valid after invoking filter's decodeHeaders() or encodeHeaders() method. If a filter has modified or deleted critical header the request should be aborted with 500 response.

Critical request header are:

• :host

Critical response headers are:

• :status