Add at rest encryption to Meterpreter payloads

gem/Rakefile

@@ -1,5 +1,6 @@
 require "bundler/gem_tasks"
 require 'openssl'
+require 'metasploit-payloads/crypto'
 
 c_source = "../c/meterpreter/"
 java_source = "../java"
@@ -52,7 +53,9 @@ def copy_files(cnf, meterpreter_dest)
       Dir.glob("#{f}/*.#{ext}").each do |bin|
         target = File.join(meterpreter_dest, File.basename(bin))
         print("Copying: #{bin} -> #{target}\n")
-        FileUtils.cp(bin, target)
+        contents = ::File.binread(::File.expand_path(bin))
+        encrypted_contents = ::MetasploitPayloads::Crypto.encrypt(plaintext: contents)
+        ::File.binwrite(::File.expand_path(target), encrypted_contents)
       end
     end
   end

gem/lib/metasploit-payloads.rb

@@ -3,6 +3,7 @@
 require 'openssl' unless defined? OpenSSL::Digest
 require 'metasploit-payloads/version' unless defined? MetasploitPayloads::VERSION
 require 'metasploit-payloads/error' unless defined? MetasploitPayloads::Error
+require 'metasploit-payloads/crypto' unless defined? MetasploitPayloads::Crypto
 
 #
 # This module dispenses Metasploit payload binary files
@@ -43,8 +44,9 @@ def self.manifest_errors
     manifest_contents.each_line do |line|
       filename, hash_type, hash = line.chomp.split(':')
       begin
+        filename = filename.sub('./data/', '')
         # self.path prepends the gem data directory, which is already present in the manifest file.
-        out_path = self.path(filename.sub('./data/', ''))
+        out_path = self.path(filename)
         # self.path can return a path to the gem data, or user's local data.
         bundled_file = out_path.start_with?(data_directory)
         if bundled_file
@@ -137,15 +139,25 @@ def self.path(*path_parts)
 
   #
   # Get the contents of any file packaged in this gem by local path and name.
+  # If the file is encrypted using ChaCha20, automatically decrypt it and return the file contents.
   #
   def self.read(*path_parts)
-    file_path = path(path_parts)
-    if file_path.nil?
-      full_path = ::File.join(path_parts)
-      raise ::MetasploitPayloads::NotFoundError, full_path, caller
+    file_path = self.path(path_parts)
+
+    begin
+      file_contents = ::File.binread(file_path)
+    rescue ::Errno::ENOENT => _e
+      raise ::MetasploitPayloads::NotFoundError, file_path, caller
+    rescue ::Errno::EACCES => _e
+      raise ::MetasploitPayloads::NotReadableError, file_path, caller
+    rescue ::StandardError => e
+      raise e
     end
 
-    ::File.binread(file_path)
+    encrypted_file = file_contents.start_with?(Crypto::ENCRYPTED_PAYLOAD_HEADER)
+    return file_contents unless encrypted_file
+
+    Crypto.decrypt(ciphertext: file_contents)
   end
 
   #

gem/lib/metasploit-payloads/crypto.rb

@@ -0,0 +1,44 @@
+require 'openssl'
+
+module MetasploitPayloads
+  module Crypto
+    CIPHER_NAME = 'chacha20'.b.freeze
+    IV = 'EncryptedPayload'.b.freeze # 16 bytes
+    KEY = 'Rapid7MetasploitEncryptedPayload'.b.freeze # 32 bytes
+    ENCRYPTED_PAYLOAD_HEADER = 'encrypted_payload_chacha20_v1'.ljust(64, '_').b.freeze
+
+    def self.encrypt(plaintext: '')
+      raise ::ArgumentError, 'Unable to encrypt plaintext: ' << plaintext, caller unless plaintext.to_s
+
+      cipher = ::OpenSSL::Cipher.new(CIPHER_NAME)
+
+      cipher.encrypt
+      cipher.iv = IV
+      cipher.key = KEY
+
+      output = ENCRYPTED_PAYLOAD_HEADER.dup
+      output << cipher.update(plaintext)
+      output << cipher.final
+
+      output
+    end
+
+    def self.decrypt(ciphertext: '')
+      raise ::ArgumentError, 'Unable to decrypt ciphertext: ' << ciphertext, caller unless ciphertext.to_s
+
+      cipher = ::OpenSSL::Cipher.new(CIPHER_NAME)
+
+      cipher.decrypt
+      cipher.iv = IV
+      cipher.key = KEY
+
+      # Remove encrypted header if present
+      ciphertext = ciphertext.sub(ENCRYPTED_PAYLOAD_HEADER, '')
+
+      output = cipher.update(ciphertext)
+      output << cipher.final
+
+      output
+    end
+  end
+end

gem/spec/metasploit_payloads/crypto_spec.rb

@@ -0,0 +1,22 @@
+require 'spec_helper'
+require 'metasploit-payloads'
+
+RSpec.describe ::MetasploitPayloads::Crypto do
+  describe '#encrypt' do
+    let(:encrypted_header) { "encrypted_payload_chacha20_v1".ljust(64, '_').b }
+    let(:plaintext) { "Hello World!".b }
+    let(:ciphertext) { encrypted_header + "\\c\xB6N\x95\xE58\x8D\xDF\xBF4c".b }
+
+    it 'can encrypt plaintext' do
+      expect(described_class.encrypt(plaintext: plaintext)).to eq ciphertext
+    end
+
+    it 'can decrypt ciphertext' do
+      expect(described_class.decrypt(ciphertext: ciphertext)).to eq plaintext
+    end
+
+    it 'is idempotent' do
+      expect(described_class.decrypt(ciphertext: described_class.encrypt(plaintext: plaintext))).to eq plaintext
+    end
+  end
+end

gem/spec/metasploit_payloads/metasploit_payloads_spec.rb

@@ -226,6 +226,8 @@
         bundled_file_path = ::MetasploitPayloads.expand(::MetasploitPayloads.data_directory, sample_file[:name])
         error = ::MetasploitPayloads::HashMismatchError.new(bundled_file_path)
         allow(::MetasploitPayloads).to receive(:path).with(sample_file[:name]).and_return(bundled_file_path)
+        # Second call to self.read takes in the splat operator
+        allow(::MetasploitPayloads).to receive(:path).with([sample_file[:name]]).and_return(bundled_file_path)
         allow(::File).to receive(:binread).with(bundled_file_path).and_return('sample_mismatched_contents')
 
         expect(subject.manifest_errors).to include({ path: bundled_file_path, error: error })
@@ -246,4 +248,34 @@
       end
     end
   end
+
+  describe '#read' do
+    let(:encrypted_header) { 'encrypted_payload_chacha20_v1' }
+    let(:raw_file) { { name: 'meterpreter.py', contents: 'sample_file_contents' } }
+    # ChaCha20 encrypted contents
+    let(:encrypted_contents) { "gg\xB7R\x96\xA00\x84\xC4\xBF5\x1D\xDBG6J\n\x86\x06\xF1" }
+    let(:encrypted_file) { { name: raw_file[:name], contents: encrypted_header + encrypted_contents } }
+
+    before :each do
+      allow(::MetasploitPayloads).to receive(:path).and_call_original
+      allow(::MetasploitPayloads).to receive(:path).with([encrypted_file[:name]]).and_return(encrypted_file[:name])
+      allow(::MetasploitPayloads).to receive(:path).with([raw_file[:name]]).and_return(raw_file[:name])
+
+      allow(::File).to receive(:binread).and_call_original
+      allow(::File).to receive(:binread).with(encrypted_file[:name]).and_return(encrypted_file[:contents])
+      allow(::File).to receive(:binread).with(raw_file[:name]).and_return(raw_file[:contents])
+    end
+
+    context 'an encrypted file' do
+      it 'returns plain-text file contents' do
+        expect(subject.read(encrypted_file[:name])).to eq(raw_file[:contents])
+      end
+    end
+
+    context 'a plain-text file' do
+      it 'returns plain-text file contents' do
+        expect(subject.read(raw_file[:name])).to eq(raw_file[:contents])
+      end
+    end
+  end
 end