client_golang is the instrumentation library for Go applications in Prometheus, and the promhttp package in client_golang provides tooling around HTTP servers and clients. In client_golang prior to version 1.11.1, 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. client_golang version 1.11.1 contains a patch for this issue. 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.