CVE-2022-21698: Uncontrolled Resource Consumption

client_golang’s HTTP server is susceptible to a Denial of Service through unbounded cardinality, and potential memory exhaustion, when handling requests with non-standard HTTP methods. In order to be affected, an instrumented software must use any of promhttp.InstrumentHandler* middleware except RequestsInFlight; not filter any specific methods (e.g GET) before middleware; pass metric with method label name to our middleware; and not have any firewall/LB/proxy that filters away requests with unknown method. Several workarounds are available, including removing the method label name from counter/gauge used in the InstrumentHandler; turning off affected promhttp handlers; adding custom middleware before promhttp handler that will sanitize the request method given by Go http.Request; and using a reverse proxy or web application firewall, configured to only allow a limited set of methods.