diff --git a/lib/vector_mcp/image_util.rb b/lib/vector_mcp/image_util.rb
index 838ab02..8df8881 100644
--- a/lib/vector_mcp/image_util.rb
+++ b/lib/vector_mcp/image_util.rb
@@ -231,29 +231,52 @@ def determine_final_mime_type(explicit_mime_type, detected_mime_type)
     #     base_directory: "/app/uploads"
     #   )
     def file_to_mcp_image_content(file_path, validate: true, max_size: DEFAULT_MAX_SIZE, base_directory: nil)
-      validate_path_safety!(file_path, base_directory) if base_directory
+      validated_path = validate_path_safety!(file_path, base_directory)
 
-      raise ArgumentError, "Image file not found: #{file_path}" unless File.exist?(file_path)
+      raise ArgumentError, "Image file not found: #{validated_path}" unless File.exist?(validated_path)
 
-      raise ArgumentError, "Image file not readable: #{file_path}" unless File.readable?(file_path)
+      raise ArgumentError, "Image file not readable: #{validated_path}" unless File.readable?(validated_path)
 
-      binary_data = File.binread(file_path)
+      binary_data = File.binread(validated_path)
       to_mcp_image_content(binary_data, validate: validate, max_size: max_size)
     end
 
-    # Validates that a file path does not escape the given base directory.
+    # Validates that a file path is safe to access.
+    #
+    # When +base_directory+ is provided, the resolved path must reside within it.
+    # When +base_directory+ is omitted, the path is still canonicalized and
+    # rejected if it contains path traversal sequences (+..+) that resolve
+    # outside the current working directory.
     #
     # @param file_path [String] The file path to validate.
-    # @param base_directory [String] The base directory boundary.
-    # @raise [ArgumentError] If the resolved path is outside base_directory.
+    # @param base_directory [String, nil] Optional base directory boundary.
+    # @return [String] The canonicalized, validated path.
+    # @raise [ArgumentError] If path traversal is detected.
     # @api private
     def validate_path_safety!(file_path, base_directory)
-      resolved_base = File.expand_path(base_directory)
-      resolved_path = File.expand_path(file_path, resolved_base)
+      if base_directory
+        resolved_base = File.expand_path(base_directory)
+        resolved_path = File.expand_path(file_path, resolved_base)
 
-      return if resolved_path.start_with?("#{resolved_base}/") || resolved_path == resolved_base
+        unless resolved_path.start_with?("#{resolved_base}/") || resolved_path == resolved_base
+          raise ArgumentError, "Path traversal detected: resolved path is outside the allowed base directory"
+        end
+      else
+        resolved_path = File.expand_path(file_path)
+
+        # Reject paths that use traversal sequences to escape upward, even without
+        # an explicit base directory.  This catches the common case of
+        # user-supplied input like "../../etc/passwd".
+        if file_path.to_s.include?("..")
+          canonical_base = File.expand_path(".")
+          unless resolved_path.start_with?("#{canonical_base}/") || resolved_path == canonical_base
+            raise ArgumentError,
+                  "Path traversal detected: '#{file_path}' resolves outside the working directory"
+          end
+        end
+      end
 
-      raise ArgumentError, "Path traversal detected: resolved path is outside the allowed base directory"
+      resolved_path
     end
 
     # Extracts image metadata from binary data.
diff --git a/lib/vector_mcp/transport/http_stream.rb b/lib/vector_mcp/transport/http_stream.rb
index e665ccb..d98ca6e 100644
--- a/lib/vector_mcp/transport/http_stream.rb
+++ b/lib/vector_mcp/transport/http_stream.rb
@@ -53,6 +53,16 @@ class HttpStream
       DEFAULT_EVENT_RETENTION = 100 # Keep last 100 events for resumability
       DEFAULT_REQUEST_TIMEOUT = 30 # Default timeout for server-initiated requests
 
+      # Default allowed origins — restrict to localhost by default for security.
+      DEFAULT_ALLOWED_ORIGINS = %w[
+        http://localhost
+        https://localhost
+        http://127.0.0.1
+        https://127.0.0.1
+        http://[::1]
+        https://[::1]
+      ].freeze
+
       # Initializes a new HTTP Stream transport.
       #
       # @param server [VectorMCP::Server] The server instance that will handle messages
@@ -62,7 +72,8 @@ class HttpStream
       # @option options [String] :path_prefix ("/mcp") The base path for HTTP endpoints
       # @option options [Integer] :session_timeout (300) Session timeout in seconds
       # @option options [Integer] :event_retention (100) Number of events to retain for resumability
-      # @option options [Array<String>] :allowed_origins (["*"]) List of allowed origins for CORS. Use ["*"] to allow all origins.
+      # @option options [Array<String>] :allowed_origins Allowed origins for CORS validation.
+      #   Defaults to localhost origins only. Pass ["*"] to allow all origins (NOT recommended for production).
       def initialize(server, options = {})
         @server = server
         @logger = server.logger
@@ -668,7 +679,13 @@ def valid_get_accept?(env)
         accept.include?("text/event-stream") || accept.include?("*/*")
       end
 
-      # Validates the Origin header for security
+      # Validates the Origin header for security.
+      #
+      # Matches are checked both exactly and as prefix (so that
+      # +http://localhost+ in the allowed list matches +http://localhost:3000+).
+      #
+      # Requests without an Origin header are allowed through because they
+      # originate from non-browser contexts (curl, server-to-server, etc.).
       #
       # @param env [Hash] The Rack environment
       # @return [Boolean] True if origin is allowed, false otherwise
@@ -678,7 +695,9 @@ def valid_origin?(env)
         origin = env["HTTP_ORIGIN"]
         return true if origin.nil? # Allow requests without Origin header (e.g., server-to-server)
 
-        @allowed_origins.include?(origin)
+        @allowed_origins.any? do |allowed|
+          origin == allowed || origin.start_with?("#{allowed}:")
+        end
       end
 
       # Logging and error handling
@@ -874,7 +893,17 @@ def initialize_configuration(options)
         @path_prefix = normalize_path_prefix(options[:path_prefix] || DEFAULT_PATH_PREFIX)
         @session_timeout = options[:session_timeout] || DEFAULT_SESSION_TIMEOUT
         @event_retention = options[:event_retention] || DEFAULT_EVENT_RETENTION
-        @allowed_origins = options[:allowed_origins] || ["*"]
+        @allowed_origins = options[:allowed_origins] || DEFAULT_ALLOWED_ORIGINS
+
+        warn_on_permissive_origins if @allowed_origins.include?("*")
+      end
+
+      # Logs a security warning when wildcard origin is configured.
+      def warn_on_permissive_origins
+        logger.warn do
+          "[SECURITY] allowed_origins includes '*', which permits cross-origin requests from any website. " \
+            "This is not recommended for production. Specify explicit origins instead."
+        end
       end
 
       # Initialize core HTTP stream components
diff --git a/spec/vector_mcp/image_util_spec.rb b/spec/vector_mcp/image_util_spec.rb
index 2c239f5..d7d8421 100644
--- a/spec/vector_mcp/image_util_spec.rb
+++ b/spec/vector_mcp/image_util_spec.rb
@@ -354,7 +354,20 @@
         end.to raise_error(ArgumentError, /Path traversal detected/)
       end
 
-      it "allows access without base_directory (backward compatible)" do
+      it "allows access without base_directory for non-traversal paths" do
+        result = described_class.file_to_mcp_image_content(temp_file.path)
+        expect(result[:type]).to eq("image")
+      end
+    end
+
+    context "without base_directory (enforced traversal rejection)" do
+      it "rejects relative paths with .. that escape the working directory" do
+        expect do
+          described_class.file_to_mcp_image_content("../../etc/passwd")
+        end.to raise_error(ArgumentError, /Path traversal detected/)
+      end
+
+      it "allows absolute paths that do not contain .." do
         result = described_class.file_to_mcp_image_content(temp_file.path)
         expect(result[:type]).to eq("image")
       end
diff --git a/spec/vector_mcp/transport/http_stream_spec.rb b/spec/vector_mcp/transport/http_stream_spec.rb
index 1c02c7b..35ffa0a 100644
--- a/spec/vector_mcp/transport/http_stream_spec.rb
+++ b/spec/vector_mcp/transport/http_stream_spec.rb
@@ -560,7 +560,7 @@
         let(:restricted_transport) { described_class.new(mock_mcp_server, allowed_origins: ["https://example.com"]) }
         let(:restricted_app) { restricted_transport }
 
-        context "with unrestricted origins (default)" do
+        context "with default origins (localhost only)" do
           it "allows requests without Origin header" do
             post "/mcp", { "jsonrpc" => "2.0", "method" => "ping" }.to_json,
                  valid_headers.merge("CONTENT_TYPE" => "application/json")
@@ -568,10 +568,44 @@
             expect(last_response.status).to eq(200)
           end
 
-          it "allows requests with any Origin header" do
+          it "allows requests from localhost origins" do
+            post "/mcp", { "jsonrpc" => "2.0", "method" => "ping" }.to_json,
+                 valid_headers.merge("CONTENT_TYPE" => "application/json", "HTTP_ORIGIN" => "http://localhost:3000")
+
+            expect(last_response.status).to eq(200)
+          end
+
+          it "allows requests from 127.0.0.1 origins" do
+            post "/mcp", { "jsonrpc" => "2.0", "method" => "ping" }.to_json,
+                 valid_headers.merge("CONTENT_TYPE" => "application/json", "HTTP_ORIGIN" => "http://127.0.0.1:8080")
+
+            expect(last_response.status).to eq(200)
+          end
+
+          it "rejects requests from non-localhost origins" do
             post "/mcp", { "jsonrpc" => "2.0", "method" => "ping" }.to_json,
                  valid_headers.merge("CONTENT_TYPE" => "application/json", "HTTP_ORIGIN" => "https://malicious.com")
 
+            expect(last_response.status).to eq(403)
+          end
+        end
+
+        context "with wildcard origins (opt-in)" do
+          let(:wildcard_transport) do
+            described_class.new(mock_mcp_server, allowed_origins: ["*"])
+          end
+          let(:app) { wildcard_transport }
+
+          before do
+            allow(wildcard_transport.session_manager).to receive(:get_or_create_session).with(session_id, anything).and_return(mock_session)
+            allow(wildcard_transport.session_manager).to receive(:get_session).with(session_id).and_return(mock_session)
+            allow(mock_session_context).to receive(:request_context=)
+          end
+
+          it "allows requests from any origin" do
+            post "/mcp", { "jsonrpc" => "2.0", "method" => "ping" }.to_json,
+                 valid_headers.merge("CONTENT_TYPE" => "application/json", "HTTP_ORIGIN" => "https://anywhere.com")
+
             expect(last_response.status).to eq(200)
           end
         end