Block wallet mode on HTTP transports to prevent CORS-based attacks

.changeset/clever-nights-enjoy.md

@@ -0,0 +1,5 @@
+---
+"@sei-js/mcp-server": patch
+---
+
+Block wallet mode on HTTP transports to prevent CORS-based attacks

packages/mcp-server/src/server/args.ts

@@ -97,7 +97,7 @@ Examples:
   Streamable HTTP transport with custom path:
     $ SERVER_TRANSPORT=streamable-http SERVER_PORT=8080 SERVER_PATH=/api/mcp npx ${packageInfo.name}
 
-  With wallet enabled:
+  With wallet enabled (STDIO transport only):
     $ WALLET_MODE=private-key PRIVATE_KEY=your_private_key_here npx ${packageInfo.name}
 
 Environment Variables:
@@ -110,6 +110,10 @@ Environment Variables:
   MAINNET_RPC_URL     Custom RPC URL for Sei mainnet (optional)
   TESTNET_RPC_URL     Custom RPC URL for Sei testnet (optional)
   DEVNET_RPC_URL      Custom RPC URL for Sei devnet (optional)
+
+Security Note:
+  Wallet mode is only supported with stdio transport. HTTP transports block
+  wallet mode to prevent cross-origin attacks from malicious websites.
 `);
 
 	program.parse();

packages/mcp-server/src/server/transport/factory.ts

@@ -9,14 +9,12 @@ export const createTransport = (config: TransportConfig): McpTransport => {
 			return new StdioTransport();
 
 		case 'streamable-http':
-			return new StreamableHttpTransport(config.port, config.host, config.path);
+			return new StreamableHttpTransport(config.port, config.host, config.path, config.walletMode);
 
 		case 'http-sse':
-			return new HttpSseTransport(config.port, config.host, config.path);
+			return new HttpSseTransport(config.port, config.host, config.path, config.walletMode);
 
 		default:
 			throw new Error(`Unsupported transport mode: ${config.mode}`);
 	}
 };
-
-

packages/mcp-server/src/server/transport/http-sse.ts

@@ -1,39 +1,35 @@
 import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 import { SSEServerTransport } from '@modelcontextprotocol/sdk/server/sse.js';
-import cors from 'cors';
 import express, { type Request, type Response } from 'express';
 import type { Server } from 'node:http';
-import type { McpTransport } from './types.js';
+import type { McpTransport, WalletMode } from './types.js';
+import { createCorsMiddleware, validateSecurityConfig } from './security.js';
 
 export class HttpSseTransport implements McpTransport {
 	readonly mode = 'http-sse' as const;
 	private app: express.Application;
 	private httpServer: Server | null = null;
 	private connections = new Map<string, SSEServerTransport>();
 	private mcpServer: McpServer | null = null;
+	private walletMode: WalletMode;
 
 	constructor(
 		private port: number,
 		private host: string,
-		private path: string
+		private path: string,
+		walletMode: WalletMode = 'disabled'
 	) {
+		this.walletMode = walletMode;
 		this.app = express();
 		this.setupMiddleware();
 		this.setupRoutes();
 	}
 
 	private setupMiddleware() {
 		this.app.use(express.json());
-		this.app.use(
-			cors({
-				origin: '*',
-				methods: ['GET', 'POST', 'OPTIONS'],
-				allowedHeaders: ['Content-Type', 'Authorization'],
-				credentials: true,
-				exposedHeaders: ['Content-Type', 'Access-Control-Allow-Origin']
-			})
-		);
-		this.app.options('*', cors());
+
+		// Secure CORS - no cross-origin allowed by default
+		this.app.use(createCorsMiddleware());
 	}
 
 	private setupRoutes() {
@@ -82,6 +78,9 @@ export class HttpSseTransport implements McpTransport {
 	}
 
 	async start(server: McpServer): Promise<void> {
+		// Block wallet mode on HTTP transports
+		validateSecurityConfig(this.mode, this.walletMode);
+
 		this.mcpServer = server;
 		return new Promise((resolve, reject) => {
 			this.httpServer = this.app.listen(this.port, this.host, () => {

packages/mcp-server/src/server/transport/security.ts

@@ -0,0 +1,45 @@
+import type { Request, Response, NextFunction, RequestHandler } from 'express';
+import type { TransportMode, WalletMode } from './types.js';
+
+/**
+ * Creates CORS middleware with secure defaults.
+ * By default, no CORS headers are set (same-origin only).
+ */
+export function createCorsMiddleware(): RequestHandler {
+	return (req: Request, res: Response, next: NextFunction) => {
+		// Handle preflight - reject cross-origin by default
+		if (req.method === 'OPTIONS') {
+			return res.sendStatus(204);
+		}
+		next();
+	};
+}
+
+/**
+ * Validates that wallet mode is not used with HTTP transports
+ * Exits the process if unsafe configuration detected
+ */
+export function validateSecurityConfig(
+	transportMode: TransportMode,
+	walletMode: WalletMode
+): void {
+	const isHttpTransport = transportMode === 'streamable-http' || transportMode === 'http-sse';
+	const isWalletEnabled = walletMode !== 'disabled';
+
+	if (isHttpTransport && isWalletEnabled) {
+		console.error('');
+		console.error('╔════════════════════════════════════════════════════════════════╗');
+		console.error('║                     SECURITY ERROR                             ║');
+		console.error('╠════════════════════════════════════════════════════════════════╣');
+		console.error('║ Wallet mode cannot be used with HTTP transports!               ║');
+		console.error('║                                                                ║');
+		console.error('║ HTTP transports expose the server to cross-origin requests,    ║');
+		console.error('║ allowing malicious websites to steal funds from your wallet.   ║');
+		console.error('║                                                                ║');
+		console.error('║ Use stdio transport instead (default, works with Claude):      ║');
+		console.error('║   $ WALLET_MODE=private-key PRIVATE_KEY=... npx @sei-js/mcp-server');
+		console.error('╚════════════════════════════════════════════════════════════════╝');
+		console.error('');
+		process.exit(1);
+	}
+}

packages/mcp-server/src/server/transport/streamable-http.ts

@@ -2,38 +2,42 @@ import express, { type Request, type Response } from 'express';
 import type { Server } from 'node:http';
 import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
 import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
-import type { McpTransport, TransportMode } from './types.js';
-import {getServer} from '../server.js';
+import type { McpTransport, TransportMode, WalletMode } from './types.js';
+import { createCorsMiddleware, validateSecurityConfig } from './security.js';
+import { getServer } from '../server.js';
 
 export class StreamableHttpTransport implements McpTransport {
 	public readonly mode: TransportMode = 'streamable-http';
 	private port: number;
 	private host: string;
 	private path: string;
+	private walletMode: WalletMode;
 	private app?: express.Express;
 	private server?: Server;
 
-	constructor(port = 8080, host = 'localhost', path = '/mcp') {
+	constructor(port = 8080, host = 'localhost', path = '/mcp', walletMode: WalletMode = 'disabled') {
 		this.port = port;
 		this.host = host;
 		this.path = path;
+		this.walletMode = walletMode;
 	}
 
 	// Note: server parameter ignored for now as this is a stateless server
 	// TODO: allow creating both stateless and stateful remote MCP servers
 	async start(_server: McpServer): Promise<void> {
+		// Block wallet mode on HTTP transports
+		validateSecurityConfig(this.mode, this.walletMode);
+
 		this.app = express();
 		this.app.use(express.json());
-		this.app.use((req, res, next) => {
-			res.header('Access-Control-Allow-Origin', '*');
-			res.header('Access-Control-Allow-Methods', 'POST, OPTIONS');
-			res.header('Access-Control-Allow-Headers', 'Content-Type');
-			if (req.method === 'OPTIONS') {
-				return res.sendStatus(200);
-			}
-			next();
-		});
+
+		// Secure CORS - no cross-origin allowed by default
+		this.app.use(createCorsMiddleware());
 
+		// Health check endpoint
+		this.app.get('/health', (_req: Request, res: Response) => {
+			res.json({ status: 'ok', timestamp: new Date().toISOString() });
+		});
 
 		this.app.post(this.path, async (req: Request, res: Response) => {
 			try {

packages/mcp-server/src/server/transport/types.ts

@@ -1,6 +1,8 @@
 import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 
 export type TransportMode = 'stdio' | 'streamable-http' | 'http-sse';
+export type WalletMode = 'disabled' | 'private-key';
+
 export interface McpTransport {
 	start(server: McpServer): Promise<void>;
 	stop(): Promise<void>;
@@ -9,7 +11,7 @@ export interface McpTransport {
 
 export interface TransportConfig {
 	mode: TransportMode;
-	walletMode: 'disabled' | 'private-key';
+	walletMode: WalletMode;
 	port: number; // Required for HTTP-based transports
 	host: string; // Required for HTTP-based transports
 	path: string; // Required for HTTP-based transports

packages/mcp-server/src/tests/server/transport/factory.test.ts

@@ -70,7 +70,7 @@ describe('Transport Factory', () => {
 
 			const transport = createTransport(config);
 
-			expect(StreamableHttpTransport).toHaveBeenCalledWith(8080, '0.0.0.0', '/api/mcp');
+			expect(StreamableHttpTransport).toHaveBeenCalledWith(8080, '0.0.0.0', '/api/mcp', 'private-key');
 			expect(transport).toBe(mockStreamableInstance);
 		});
 
@@ -88,7 +88,7 @@ describe('Transport Factory', () => {
 
 			const transport = createTransport(config);
 
-			expect(HttpSseTransport).toHaveBeenCalledWith(9000, '127.0.0.1', '/sse');
+			expect(HttpSseTransport).toHaveBeenCalledWith(9000, '127.0.0.1', '/sse', 'disabled');
 			expect(transport).toBe(mockSseInstance);
 		});
 
@@ -123,7 +123,7 @@ describe('Transport Factory', () => {
 
 				const transport = createTransport(config);
 
-				expect(StreamableHttpTransport).toHaveBeenCalledWith(params.port, params.host, params.path);
+				expect(StreamableHttpTransport).toHaveBeenCalledWith(params.port, params.host, params.path, 'disabled');
 				expect(transport).toBe(mockInstance);
 
 				jest.clearAllMocks();
@@ -145,7 +145,7 @@ describe('Transport Factory', () => {
 
 			const transport1 = createTransport(config1);
 
-			expect(HttpSseTransport).toHaveBeenCalledWith(1, '::1', '/');
+			expect(HttpSseTransport).toHaveBeenCalledWith(1, '::1', '/', 'private-key');
 			expect(transport1).toBe(mockInstance1);
 
 			jest.clearAllMocks();
@@ -164,7 +164,7 @@ describe('Transport Factory', () => {
 
 			const transport2 = createTransport(config2);
 
-			expect(StreamableHttpTransport).toHaveBeenCalledWith(65535, '0.0.0.0', '/very/long/path/to/test/edge/cases');
+			expect(StreamableHttpTransport).toHaveBeenCalledWith(65535, '0.0.0.0', '/very/long/path/to/test/edge/cases', 'disabled');
 			expect(transport2).toBe(mockInstance2);
 		});
 	});

packages/mcp-server/src/tests/server/transport/http-sse.test.ts

@@ -16,7 +16,10 @@ jest.mock('express', () => {
 	return express;
 });
 
-jest.mock('cors', () => jest.fn(() => 'cors-middleware'));
+jest.mock('../../../server/transport/security.js', () => ({
+	createCorsMiddleware: jest.fn(() => 'cors-middleware'),
+	validateSecurityConfig: jest.fn()
+}));
 
 jest.mock('@modelcontextprotocol/sdk/server/sse.js', () => ({
 	SSEServerTransport: jest.fn()
@@ -27,7 +30,8 @@ describe('HttpSseTransport', () => {
 	let mockExpress: jest.MockedFunction<any>;
 	let mockApp: any;
 	let mockServer: any;
-	let mockCors: jest.MockedFunction<any>;
+	let mockCreateCorsMiddleware: jest.MockedFunction<any>;
+	let mockValidateSecurityConfig: jest.MockedFunction<any>;
 	let mockSSEServerTransport: jest.MockedFunction<any>;
 	let mockTransport: any;
 	let mockMcpServer: any;
@@ -38,11 +42,12 @@ describe('HttpSseTransport', () => {
 
 		// Import mocked modules
 		const expressModule = await import('express');
-		const corsModule = await import('cors');
+		const securityModule = await import('../../../server/transport/security.js');
 		const { SSEServerTransport } = await import('@modelcontextprotocol/sdk/server/sse.js');
 
 		mockExpress = expressModule.default as jest.MockedFunction<any>;
-		mockCors = corsModule.default as jest.MockedFunction<any>;
+		mockCreateCorsMiddleware = securityModule.createCorsMiddleware as jest.MockedFunction<any>;
+		mockValidateSecurityConfig = securityModule.validateSecurityConfig as jest.MockedFunction<any>;
 		mockSSEServerTransport = SSEServerTransport as jest.MockedFunction<any>;
 
 		// Setup mock objects
@@ -70,7 +75,7 @@ describe('HttpSseTransport', () => {
 		// Configure mocks
 		mockExpress.mockReturnValue(mockApp);
 		mockExpress.json = jest.fn().mockReturnValue('json-middleware');
-		mockCors.mockReturnValue('cors-middleware');
+		mockCreateCorsMiddleware.mockReturnValue('cors-middleware');
 		mockSSEServerTransport.mockImplementation(() => mockTransport);
 
 		// Import the class after mocks are set up
@@ -96,14 +101,8 @@ describe('HttpSseTransport', () => {
 
 			expect(mockExpress).toHaveBeenCalled();
 			expect(mockApp.use).toHaveBeenCalledWith('json-middleware');
-			expect(mockCors).toHaveBeenCalledWith({
-				origin: '*',
-				methods: ['GET', 'POST', 'OPTIONS'],
-				allowedHeaders: ['Content-Type', 'Authorization'],
-				credentials: true,
-				exposedHeaders: ['Content-Type', 'Access-Control-Allow-Origin']
-			});
-			expect(mockApp.options).toHaveBeenCalledWith('*', 'cors-middleware');
+			expect(mockCreateCorsMiddleware).toHaveBeenCalled();
+			expect(mockApp.use).toHaveBeenCalledWith('cors-middleware');
 			expect(mockApp.get).toHaveBeenCalledWith('/health', expect.any(Function));
 			expect(mockApp.get).toHaveBeenCalledWith('/sse', expect.any(Function));
 			expect(mockApp.post).toHaveBeenCalledWith('/sse/message', expect.any(Function));