Fix frozen string error in FTP mixin when using frozen_string_literal: true

lib/msf/core/exploit/remote/ftp.rb

@@ -38,7 +38,7 @@ def initialize(info = {})
     register_autofilter_ports([ 21, 2121])
     register_autofilter_services(%W{ ftp })
 
-    @ftpbuff = ""
+    @ftpbuff = +""
 
   end
 
@@ -326,7 +326,7 @@ def recv_ftp_resp(nsock = self.sock)
     left = ""
     if !@ftpbuff.empty?
       left << @ftpbuff
-      @ftpbuff = ""
+      @ftpbuff = +""
     end
     while true
       data = nsock.get_once(-1, ftp_timeout)

test/modules/test_ftp_frozen_string.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'test/unit'
+require 'msf/core'
+
+class TestFtpMixinFrozenString < Test::Unit::TestCase
+  include Msf
+
+  def setup
+    @module = Msf::Module.new
+    @module.extend(Exploit::Remote::Ftp)
+  end
+
+  def test_ftpbuff_is_mutable
+    # Initialize the FTP mixin
+    @module.send(:initialize, {})
+
+    # Access the internal @ftpbuff variable
+    ftpbuff = @module.instance_variable_get(:@ftpbuff)
+
+    # Verify it's not frozen
+    assert_not_predicate(ftpbuff, :frozen?, "@ftpbuff should be mutable even with frozen_string_literal: true")
+
+    # Verify we can modify it
+    assert_nothing_raised do
+      ftpbuff << "test data"
+    end
+  end
+
+  def test_recv_ftp_resp_with_frozen_string_literal
+    # This test verifies that recv_ftp_resp works correctly
+    # when the module uses frozen_string_literal: true
+
+    # Mock the socket
+    mock_socket = Object.new
+    def mock_socket.get
+      "220 Welcome\r\n"
+    end
+
+    @module.instance_variable_set(:@sock, mock_socket)
+
+    # This should not raise FrozenError
+    assert_nothing_raised do
+      result = @module.send(:recv_ftp_resp)
+      assert_equal("220 Welcome", result)
+    end
+  end
+end