| Description: | 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.
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