CVE-2022-21698

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.