Go before 1.13.13 and 1.14.x before 1.14.5 has a data race in some net/http servers, as demonstrated by the httputil.ReverseProxy Handler, because it reads a request body and writes a response at the same time.
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.