diff --git a/packages/cli-server-api/package.json b/packages/cli-server-api/package.json
index 4610149de..e4a015479 100644
--- a/packages/cli-server-api/package.json
+++ b/packages/cli-server-api/package.json
@@ -16,6 +16,7 @@
     "open": "^6.2.0",
     "pretty-format": "^29.7.0",
     "serve-static": "^1.13.1",
+    "strict-url-sanitise": "0.0.1",
     "ws": "^6.2.3"
   },
   "devDependencies": {
diff --git a/packages/cli-server-api/src/__tests__/openURLMiddleware.test.ts b/packages/cli-server-api/src/__tests__/openURLMiddleware.test.ts
new file mode 100644
index 000000000..0f26e8274
--- /dev/null
+++ b/packages/cli-server-api/src/__tests__/openURLMiddleware.test.ts
@@ -0,0 +1,117 @@
+import http from 'http';
+import {Readable} from 'stream';
+import open from 'open';
+import openURLMiddleware from '../openURLMiddleware';
+
+jest.mock('open');
+
+function createMockRequest(method: string, body: object): http.IncomingMessage {
+  const bodyStr = JSON.stringify(body);
+  const readable = new Readable();
+  readable.push(bodyStr);
+  readable.push(null);
+
+  return Object.assign(readable, {
+    method,
+    url: '/',
+    headers: {
+      'content-type': 'application/json',
+      'content-length': String(Buffer.byteLength(bodyStr)),
+    },
+  }) as unknown as http.IncomingMessage;
+}
+
+describe('openURLMiddleware', () => {
+  let res: jest.Mocked<http.ServerResponse>;
+  let next: jest.Mock;
+
+  beforeEach(() => {
+    res = {
+      writeHead: jest.fn(),
+      end: jest.fn(),
+      setHeader: jest.fn(),
+    } as any;
+
+    next = jest.fn();
+    jest.clearAllMocks();
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  test('should return 400 for non-string URL', (done) => {
+    const req = createMockRequest('POST', {url: 123});
+
+    res.end = jest.fn(() => {
+      try {
+        expect(open).not.toHaveBeenCalled();
+        expect(res.writeHead).toHaveBeenCalledWith(400);
+        expect(res.end).toHaveBeenCalledWith('URL must be a string');
+        done();
+      } catch (error) {
+        done(error);
+      }
+    }) as any;
+
+    openURLMiddleware(req, res, next);
+  });
+
+  // CVE-2025-11953
+  test('should reject malicious URL with invalid hostname', (done) => {
+    const maliciousUrl = 'https://www.$(calc.exe).com/foo';
+    const req = createMockRequest('POST', {url: maliciousUrl});
+
+    res.end = jest.fn(() => {
+      try {
+        expect(open).not.toHaveBeenCalled();
+        expect(res.writeHead).toHaveBeenCalledWith(400);
+        expect(res.end).toHaveBeenCalledWith('Invalid URL');
+        done();
+      } catch (error) {
+        done(error);
+      }
+    }) as any;
+
+    openURLMiddleware(req, res, next);
+  });
+
+  // CVE-2025-11953
+  test('should reject URL with Windows pipe separator', (done) => {
+    const maliciousUrl = 'https://evil.com?|calc.exe';
+    const req = createMockRequest('POST', {url: maliciousUrl});
+
+    res.end = jest.fn(() => {
+      try {
+        expect(open).not.toHaveBeenCalled();
+        expect(res.writeHead).toHaveBeenCalledWith(400);
+        expect(res.end).toHaveBeenCalledWith('Invalid URL');
+        done();
+      } catch (error) {
+        done(error);
+      }
+    }) as any;
+
+    openURLMiddleware(req, res, next);
+  });
+
+  // CVE-2025-11953
+  test('should reject URL with Windows command exfiltration', (done) => {
+    // Encodes to reveal %BETA% env var
+    const maliciousUrl = 'https://example.com/?a=%¾TA%';
+    const req = createMockRequest('POST', {url: maliciousUrl});
+
+    res.end = jest.fn(() => {
+      try {
+        expect(open).not.toHaveBeenCalled();
+        expect(res.writeHead).toHaveBeenCalledWith(400);
+        expect(res.end).toHaveBeenCalledWith('Invalid URL');
+        done();
+      } catch (error) {
+        done(error);
+      }
+    }) as any;
+
+    openURLMiddleware(req, res, next);
+  });
+});
diff --git a/packages/cli-server-api/src/openURLMiddleware.ts b/packages/cli-server-api/src/openURLMiddleware.ts
index 588600790..14d5eae1a 100644
--- a/packages/cli-server-api/src/openURLMiddleware.ts
+++ b/packages/cli-server-api/src/openURLMiddleware.ts
@@ -10,6 +10,7 @@ import type {IncomingMessage, ServerResponse} from 'http';
 import {json} from 'body-parser';
 import connect from 'connect';
 import open from 'open';
+import {sanitizeUrl} from 'strict-url-sanitise';
 
 /**
  * Open a URL in the system browser.
@@ -31,20 +32,22 @@ async function openURLMiddleware(
 
     const {url} = req.body as {url: string};
 
+    if (typeof url !== 'string') {
+      res.writeHead(400);
+      res.end('URL must be a string');
+      return;
+    }
+
+    let sanitizedUrl: string;
     try {
-      const parsedUrl = new URL(url);
-      if (parsedUrl.protocol !== 'http:' && parsedUrl.protocol !== 'https:') {
-        res.writeHead(400);
-        res.end('Invalid URL protocol');
-        return;
-      }
-    } catch (error) {
+      sanitizedUrl = sanitizeUrl(url);
+    } catch {
       res.writeHead(400);
-      res.end('Invalid URL format');
+      res.end('Invalid URL');
       return;
     }
 
-    await open(url);
+    await open(sanitizedUrl);
 
     res.writeHead(200);
     res.end();
diff --git a/yarn.lock b/yarn.lock
index 09cccd258..222f1725c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9703,6 +9703,11 @@ stream-buffers@2.2.x:
   resolved "https://registry.yarnpkg.com/stream-buffers/-/stream-buffers-2.2.0.tgz#91d5f5130d1cef96dcfa7f726945188741d09ee4"
   integrity sha512-uyQK/mx5QjHun80FLJTfaWE7JtwfRMKBLkMne6udYOmvH0CawotVa7TfgYHzAnpphn4+TweIx1QKMnRIbipmUg==
 
+strict-url-sanitise@0.0.1:
+  version "0.0.1"
+  resolved "https://registry.yarnpkg.com/strict-url-sanitise/-/strict-url-sanitise-0.0.1.tgz#10cfac63c9dfdd856d98ab9f76433dad5ce99e0c"
+  integrity sha512-nuFtF539K8jZg3FjaWH/L8eocCR6gegz5RDOsaWxfdbF5Jqr2VXWxZayjTwUzsWJDC91k2EbnJXp6FuWW+Z4hg==
+
 string-argv@^0.3.1:
   version "0.3.1"
   resolved "https://registry.yarnpkg.com/string-argv/-/string-argv-0.3.1.tgz#95e2fbec0427ae19184935f816d74aaa4c5c19da"