diff --git a/Changes.md b/Changes.md
index 261a6b579..92ccfca0a 100644
--- a/Changes.md
+++ b/Changes.md
@@ -9,6 +9,7 @@ HEAD
 - Ensure `Rack::ContentLength` is loaded as middleware for correct Web UI responses [#4541]
 - Avoid exception dumping SSL store in Redis connection logging [#4532]
 - Better error messages in Sidekiq::Client [#4549]
+- Vendor rack-protection/authenticity_token middleware [#4588]
 
 6.0.7
 ---------
diff --git a/Gemfile.lock b/Gemfile.lock
index 743e63e58..96a13630a 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -4,7 +4,6 @@ PATH
     sidekiq (6.0.7)
       connection_pool (>= 2.2.2)
       rack (~> 2.0)
-      rack-protection (>= 2.0.0)
       redis (>= 4.1.0)
 
 GEM
@@ -117,8 +116,6 @@ GEM
       byebug (~> 11.0)
       pry (~> 0.10)
     rack (2.2.2)
-    rack-protection (2.0.8.1)
-      rack
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (6.0.3.1)
diff --git a/lib/sidekiq/web.rb b/lib/sidekiq/web.rb
index 3422bc510..f989ba79f 100644
--- a/lib/sidekiq/web.rb
+++ b/lib/sidekiq/web.rb
@@ -10,8 +10,8 @@
 require "sidekiq/web/router"
 require "sidekiq/web/action"
 require "sidekiq/web/application"
+require "sidekiq/web/authenticity_token"
 
-require "rack/protection"
 require "rack/content_length"
 
 require "rack/builder"
@@ -155,8 +155,8 @@ def using?(middleware)
     def build_sessions
       middlewares = self.middlewares
 
-      unless using?(::Rack::Protection) || ENV["RACK_ENV"] == "test"
-        middlewares.unshift [[::Rack::Protection, {use: :authenticity_token}], nil]
+      unless using?(AuthenticityToken) || ENV["RACK_ENV"] == "test"
+        middlewares.unshift [[AuthenticityToken], nil]
       end
 
       s = sessions
diff --git a/lib/sidekiq/web/authenticity_token.rb b/lib/sidekiq/web/authenticity_token.rb
new file mode 100644
index 000000000..80253d8b7
--- /dev/null
+++ b/lib/sidekiq/web/authenticity_token.rb
@@ -0,0 +1,254 @@
+# this file came from the sinatra/rack-protection project
+#
+# The MIT License (MIT)
+#
+# Copyright (c) 2011-2017 Konstantin Haase
+# Copyright (c) 2015-2017 Zachary Scott
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# 'Software'), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+require "securerandom"
+require "base64"
+require "rack/request"
+
+module Sidekiq
+  class Web
+    class AuthenticityToken
+      DEFAULT_OPTIONS = {
+        reaction: :default_reaction, logging: true,
+        message: "Forbidden", encryptor: Digest::SHA1,
+        session_key: "rack.session", status: 403,
+        allow_empty_referrer: true,
+        report_key: "protection.failed",
+        html_types: %w[text/html application/xhtml text/xml application/xml]
+      }
+
+      attr_reader :app, :options
+
+      def self.default_options(options)
+        define_method(:default_options) { DEFAULT_OPTIONS.merge(options) }
+      end
+
+      def self.default_reaction(reaction)
+        alias_method(:default_reaction, reaction)
+      end
+
+      def default_options
+        DEFAULT_OPTIONS
+      end
+
+      def initialize(app, options = {})
+        @app, @options = app, default_options.merge(options)
+      end
+
+      def safe?(env)
+        %w[GET HEAD OPTIONS TRACE].include? env["REQUEST_METHOD"]
+      end
+
+      def call(env)
+        unless accepts? env
+          instrument env
+          result = react env
+        end
+        result || app.call(env)
+      end
+
+      def react(env)
+        result = send(options[:reaction], env)
+        result if (Array === result) && (result.size == 3)
+      end
+
+      def warn(env, message)
+        return unless options[:logging]
+        l = options[:logger] || env["rack.logger"] || ::Logger.new(env["rack.errors"])
+        l.warn(message)
+      end
+
+      def instrument(env)
+        return unless (i = options[:instrumenter])
+        env["rack.protection.attack"] = self.class.name.split("::").last.downcase
+        i.instrument("rack.protection", env)
+      end
+
+      def deny(env)
+        warn env, "attack prevented by #{self.class}"
+        [options[:status], {"Content-Type" => "text/plain"}, [options[:message]]]
+      end
+
+      def report(env)
+        warn env, "attack reported by #{self.class}"
+        env[options[:report_key]] = true
+      end
+
+      def session?(env)
+        env.include? options[:session_key]
+      end
+
+      def session(env)
+        return env[options[:session_key]] if session? env
+        fail "you need to set up a session middleware *before* #{self.class}"
+      end
+
+      def drop_session(env)
+        session(env).clear if session? env
+      end
+
+      def referrer(env)
+        ref = env["HTTP_REFERER"].to_s
+        return if !options[:allow_empty_referrer] && ref.empty?
+        URI.parse(ref).host || Rack::Request.new(env).host
+      rescue URI::InvalidURIError
+      end
+
+      def origin(env)
+        env["HTTP_ORIGIN"] || env["HTTP_X_ORIGIN"]
+      end
+
+      def random_string(secure = defined? SecureRandom)
+        secure ? SecureRandom.hex(16) : "%032x" % rand(2**128 - 1)
+      rescue NotImplementedError
+        random_string false
+      end
+
+      def encrypt(value)
+        options[:encryptor].hexdigest value.to_s
+      end
+
+      def secure_compare(a, b)
+        Rack::Utils.secure_compare(a.to_s, b.to_s)
+      end
+
+      def html?(headers)
+        return false unless (header = headers.detect { |k, v| k.downcase == "content-type" })
+        options[:html_types].include? header.last[/^\w+\/\w+/]
+      end
+
+      TOKEN_LENGTH = 32
+
+      default_options authenticity_param: "authenticity_token",
+                      allow_if: nil
+
+      def self.token(session)
+        new(nil).mask_authenticity_token(session)
+      end
+
+      def self.random_token
+        SecureRandom.base64(TOKEN_LENGTH)
+      end
+
+      def accepts?(env)
+        session = session env
+        set_token(session)
+
+        safe?(env) ||
+          valid_token?(session, env["HTTP_X_CSRF_TOKEN"]) ||
+          valid_token?(session, Rack::Request.new(env).params[options[:authenticity_param]]) ||
+          options[:allow_if]&.call(env)
+      end
+
+      def mask_authenticity_token(session)
+        token = set_token(session)
+        mask_token(token)
+      end
+
+      private
+
+      def set_token(session)
+        session[:csrf] ||= self.class.random_token
+      end
+
+      # Checks the client's masked token to see if it matches the
+      # session token.
+      def valid_token?(session, token)
+        return false if token.nil? || token.empty?
+
+        begin
+          token = decode_token(token)
+        rescue ArgumentError # encoded_masked_token is invalid Base64
+          return false
+        end
+
+        # See if it's actually a masked token or not. We should be able
+        # to handle any unmasked tokens that we've issued without error.
+
+        if unmasked_token?(token)
+          compare_with_real_token token, session
+
+        elsif masked_token?(token)
+          token = unmask_token(token)
+
+          compare_with_real_token token, session
+
+        else
+          false # Token is malformed
+        end
+      end
+
+      # Creates a masked version of the authenticity token that varies
+      # on each request. The masking is used to mitigate SSL attacks
+      # like BREACH.
+      def mask_token(token)
+        token = decode_token(token)
+        one_time_pad = SecureRandom.random_bytes(token.length)
+        encrypted_token = xor_byte_strings(one_time_pad, token)
+        masked_token = one_time_pad + encrypted_token
+        encode_token(masked_token)
+      end
+
+      # Essentially the inverse of +mask_token+.
+      def unmask_token(masked_token)
+        # Split the token into the one-time pad and the encrypted
+        # value and decrypt it
+        token_length = masked_token.length / 2
+        one_time_pad = masked_token[0...token_length]
+        encrypted_token = masked_token[token_length..-1]
+        xor_byte_strings(one_time_pad, encrypted_token)
+      end
+
+      def unmasked_token?(token)
+        token.length == TOKEN_LENGTH
+      end
+
+      def masked_token?(token)
+        token.length == TOKEN_LENGTH * 2
+      end
+
+      def compare_with_real_token(token, session)
+        secure_compare(token, real_token(session))
+      end
+
+      def real_token(session)
+        decode_token(session[:csrf])
+      end
+
+      def encode_token(token)
+        Base64.strict_encode64(token)
+      end
+
+      def decode_token(token)
+        Base64.strict_decode64(token)
+      end
+
+      def xor_byte_strings(s1, s2)
+        s1.bytes.zip(s2.bytes).map { |(c1, c2)| c1 ^ c2 }.pack("c*")
+      end
+    end
+  end
+end
diff --git a/sidekiq.gemspec b/sidekiq.gemspec
index 510f8cb5b..808b57052 100644
--- a/sidekiq.gemspec
+++ b/sidekiq.gemspec
@@ -17,5 +17,4 @@ Gem::Specification.new do |gem|
   gem.add_dependency "redis", ">= 4.1.0"
   gem.add_dependency "connection_pool", ">= 2.2.2"
   gem.add_dependency "rack", "~> 2.0"
-  gem.add_dependency "rack-protection", ">= 2.0.0"
 end