Check gems that can be affected by http://blog.rubygems.org/2016/04/06/gem-replacement-vulnerability-and-mitigation.html

check_gems.rb

#!/usr/bin/env ruby

require 'rest-client'
require 'bundler'

CHECK_GEMS_BEFORE = Time.parse("Feb 8, 2015")

def check_bundler
  gems = Bundler::LockfileParser.new(Bundler.read_file("Gemfile.lock"))
  gems.specs.each do |spec|
    gem_name = spec.name
    version = spec.version.to_s
    next unless spec.source.kind_of?(Bundler::Source::Rubygems)

    rubygems = spec.source.remotes.find {|r| r.to_s =~ /rubygems\.org/ }
    if gem_name !~ /-/ || rubygems == nil
      next
    end

    check_gem(gem_name, version)
  end
end

def check_local_gems
  Gem::Specification.each do |gem|
    check_gem(gem.name, gem.version.to_s)
  end
end

def check_gem(gem_name, version)
  print "Checking #{gem_name} #{version}"

  response = RestClient.get("https://rubygems.org/api/v1/versions/#{gem_name}.json") {|r| r }
  if response.code != 200
    puts " [NOT FOUND]"
    return
  end

  gem_data = JSON.parse(response)
  gem = gem_data.find {|gd| gd["number"] == version }

  if !gem
    puts " [NOT FOUND]"
    return
  end

  created_at = Time.parse(gem["created_at"])
  if created_at < CHECK_GEMS_BEFORE
    puts " [UNSAFE]"
  else
    puts " [SAFE]"
  end
end

if File.exist?("Gemfile.lock")
  check_bundler
else
  check_local_gems
end