Fix path traversal bug in router (#2398)

* fix path traversal bug in router

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

* add tests

Signed-off-by: Jari Kolehmainen <jari.kolehmainen@gmail.com>

src/main/__test__/router.test.ts

@@ -0,0 +1,40 @@
+import { Router } from "../router";
+
+const staticRoot = __dirname;
+
+class TestRouter extends Router {
+  protected resolveStaticRootPath() {
+    return staticRoot;
+  }
+}
+
+describe("Router", () => {
+  it("blocks path traversal attacks", async () => {
+    const router = new TestRouter();
+    const res = {
+      statusCode: 200,
+      end: jest.fn()
+    };
+
+    await router.handleStaticFile("../index.ts", res as any, {} as any, 0);
+
+    expect(res.statusCode).toEqual(404);
+  });
+
+  it("serves files under static root", async () => {
+    const router = new TestRouter();
+    const res = {
+      statusCode: 200,
+      write: jest.fn(),
+      setHeader: jest.fn(),
+      end: jest.fn()
+    };
+    const req = {
+      url: ""
+    };
+
+    await router.handleStaticFile("router.test.ts", res as any, req as any, 0);
+
+    expect(res.statusCode).toEqual(200);
+  });
+});

src/main/router.ts

@@ -40,10 +40,16 @@ export interface LensApiRequest<P = any> {
 
 export class Router {
   protected router: any;
+  protected staticRootPath: string;
 
   public constructor() {
     this.router = new Call.Router();
     this.addRoutes();
+    this.staticRootPath = this.resolveStaticRootPath();
+  }
+
+  protected resolveStaticRootPath() {
+    return path.resolve(__static);
   }
 
   public async route(cluster: Cluster, req: http.IncomingMessage, res: http.ServerResponse): Promise<boolean> {
@@ -102,7 +108,15 @@ export class Router {
   }
 
   async handleStaticFile(filePath: string, res: http.ServerResponse, req: http.IncomingMessage, retryCount = 0) {
-    const asset = path.join(__static, filePath);
+    const asset = path.join(this.staticRootPath, filePath);
+    const normalizedFilePath = path.resolve(asset);
+
+    if (!normalizedFilePath.startsWith(this.staticRootPath)) {
+      res.statusCode = 404;
+      res.end();
+
+      return;
+    }
 
     try {
       const filename = path.basename(req.url);