For ValidateRequestBody the whole body of the request gets loaded into memory via io.ReadAll (1)
The default FileBodyDecoder(2) then also just string()s the data and returns it again
In my application this, and the following validation causes a memory usage if around 10GB when uploading a 1GB file.
From what I can tell ValidateRequestBody doesn't do any useful work on application/octet-stream data(correct me if I'm wrong please)
(1) https://github.com/getkin/kin-openapi/blob/master/openapi3filter/validate_request.go#L269
(2) https://github.com/getkin/kin-openapi/blob/master/openapi3filter/req_resp_decoder.go#L1556