fix(cli): restrict stdio MCP environment inheritance

extensions/cli/src/services/MCPService.test.ts

@@ -57,6 +57,7 @@ describe("MCPService", () => {
 
   afterEach(async () => {
     vi.clearAllMocks();
+    vi.unstubAllEnvs();
     await mcpService.cleanup();
   });
 
@@ -218,6 +219,39 @@ describe("MCPService", () => {
       ).resolves.not.toThrow();
     });
 
+    it("should not forward ambient environment variables to stdio servers", async () => {
+      vi.stubEnv("CONTINUE_MCP_TEST_SECRET", "must-not-be-inherited");
+      const { StdioClientTransport } = await import(
+        "@modelcontextprotocol/sdk/client/stdio.js"
+      );
+      const stdioAssistant: AssistantConfig = {
+        name: "stdio-assistant",
+        version: "1.0.0",
+        mcpServers: [
+          {
+            name: "stdio-server",
+            command: "node",
+            env: { EXPLICIT_MCP_VALUE: "allowed" },
+          },
+        ],
+      } as AssistantConfig;
+
+      await mcpService.initialize(stdioAssistant);
+
+      expect(StdioClientTransport).toHaveBeenCalledWith(
+        expect.objectContaining({
+          env: { EXPLICIT_MCP_VALUE: "allowed" },
+        }),
+      );
+      expect(StdioClientTransport).not.toHaveBeenCalledWith(
+        expect.objectContaining({
+          env: expect.objectContaining({
+            CONTINUE_MCP_TEST_SECRET: "must-not-be-inherited",
+          }),
+        }),
+      );
+    });
+
     it("should create HttpsAgent when verifySsl is false for SSE transport", async () => {
       const { SSEClientTransport } = await import(
         "@modelcontextprotocol/sdk/client/sse.js"

extensions/cli/src/services/mcpTransports.ts

@@ -74,19 +74,14 @@ export function constructStdioTransport(
   serverConfig: StdioMcpServer,
   connection: MCPConnectionInfo,
 ): StdioClientTransport {
-  const env: Record<string, string> = serverConfig.env || {};
-  if (process.env) {
-    for (const [key, value] of Object.entries(process.env)) {
-      if (!(key in env) && !!value) {
-        env[key] = value;
-      }
-    }
-  }
-
   const transport = new StdioClientTransport({
     command: serverConfig.command,
     args: serverConfig.args || [],
-    env,
+    // The MCP SDK adds its platform-safe default environment (for example
+    // PATH and HOME). Only add variables the user explicitly configured;
+    // forwarding process.env would expose unrelated credentials to every
+    // stdio MCP server.
+    env: serverConfig.env,
     cwd: serverConfig.cwd,
     stderr: "pipe",
   });