node_exporter -- bypass security with cache poisoning

Prometheus team reports:

  Prometheus and its exporters can be secured by a web.yml file that
  specifies usernames and hashed passwords for basic authentication.
  Passwords are hashed with bcrypt, which means that even if you have
  access to the hash, it is very hard to find the original password
  back. Passwords are hashed with bcrypt, which means that even if you
  have access to the hash, it is very hard to find the original
  password back. However, a flaw in the way this mechanism was
  implemented in the exporter toolkit makes it possible with people
  who know the hashed password to authenticate against Prometheus.
  A request can be forged by an attacker to poison the internal cache
  used to cache the computation of hashes and make subsequent requests
  successful. This cache is used in both happy and unhappy scenarios
  in order to limit side channel attacks that could tell an attacker
  if a user is present in the file or not.