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feat(brainstorm-server): gate every endpoint behind a per-session key

Browse Source 
The companion server is reachable by any local browser tab (default loopback
bind) and by any host that can route to it (remote --host bind). It served
screens, files, and accepted event-injecting WebSocket connections with no
authentication, so a malicious browser tab or a direct remote client could read
brainstorm content or inject events that the agent reads as the user's input
(prompt injection into a live session).

Generate a per-session secret token, carry it in the served URL as ?key=, and
mirror it into an HttpOnly SameSite=Strict per-port cookie on first load so
same-origin subresources and the WebSocket handshake authenticate automatically.
Every HTTP request and WebSocket upgrade now requires a valid key (query or
cookie, constant-time compared); unauthenticated requests get a friendly 403
explaining they need the full URL. A secret authenticates the client uniformly
across loopback, tunnel, and remote binds and defeats DNS rebinding, which a
Host/Origin allowlist cannot.

Also guard handleMessage against a null JSON payload that crashed the process.

Tests: new auth.test.js (13 cases) covering the key on /, /files/*, and WS plus
cookie bootstrap and the null-payload guard; server.test.js threads the key;
ws-protocol.test.js + auth.test.js wired into npm test.

Closes #1014
Refs #1110, #1553, #1504
This commit is contained in:
Jesse Vincent
2026-06-09 12:22:53 -07:00
parent 3e3c10e671
commit e3fe480b29
5 changed files with 308 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

84
skills/brainstorming/scripts/server.cjs
View File

@@ -104,6 +104,15 @@ const CONTENT_DIR = path.join(SESSION_DIR, 'content');
const STATE_DIR = path.join(SESSION_DIR, 'state');
let ownerPid = process.env.BRAINSTORM_OWNER_PID ? Number(process.env.BRAINSTORM_OWNER_PID) : null;
// Per-session secret key. The companion is reachable by any local browser tab
// and, when bound to a non-loopback host, by any host that can route to it.
// The key authenticates the real client uniformly across loopback, tunnel, and
// remote binds — and defeats DNS rebinding — where a Host/Origin allowlist
// cannot. It rides the served URL as ?key= and is mirrored into a cookie on
// first load so same-origin subresources and the WebSocket carry it for free.
const TOKEN = process.env.BRAINSTORM_TOKEN || crypto.randomBytes(32).toString('hex');
const COOKIE_NAME = 'brainstorm-key-' + PORT;
const MIME_TYPES = {
'.html': 'text/html', '.css': 'text/css', '.js': 'application/javascript',
'.json': 'application/json', '.png': 'image/png', '.jpg': 'image/jpeg',
@@ -121,6 +130,16 @@ h1 { color: #333; } p { color: #666; }</style>
<body><h1>Brainstorm Companion</h1>
<p>Waiting for the agent to push a screen...</p></body></html>`;
const FORBIDDEN_PAGE = `<!DOCTYPE html>
<html>
<head><meta charset="utf-8"><title>Session key required</title>
<style>body { font-family: system-ui, sans-serif; padding: 2rem; max-width: 800px; margin: 0 auto; }
h1 { color: #333; } p { color: #666; } code { background: #f0f0f0; padding: 0.1em 0.3em; border-radius: 4px; }</style>
</head>
<body><h1>Session key required</h1>
<p>This page needs the full URL your coding agent gave you, including the
<code>?key=&hellip;</code> part. Copy the complete URL and open it again.</p></body></html>`;
const frameTemplate = fs.readFileSync(path.join(__dirname, 'frame-template.html'), 'utf-8');
const helperScript = fs.readFileSync(path.join(__dirname, 'helper.js'), 'utf-8');
const helperInjection = '<script>\n' + helperScript + '\n</script>';
@@ -147,11 +166,64 @@ function getNewestScreen() {
return files.length > 0 ? files[0].path : null;
}
// ========== Authentication ==========
function timingSafeEqualStr(a, b) {
const ab = Buffer.from(String(a));
const bb = Buffer.from(String(b));
if (ab.length !== bb.length) return false;
return crypto.timingSafeEqual(ab, bb);
}
function parseCookies(header) {
const out = {};
if (!header) return out;
for (const part of header.split(';')) {
const eq = part.indexOf('=');
if (eq < 0) continue;
out[part.slice(0, eq).trim()] = part.slice(eq + 1).trim();
}
return out;
}
// A request is authorized if it carries the session key as ?key= or as the
// session cookie. Both are compared in constant time.
function isAuthorized(req) {
const q = req.url.indexOf('?');
if (q >= 0) {
const key = new URLSearchParams(req.url.slice(q + 1)).get('key');
if (key && timingSafeEqualStr(key, TOKEN)) return true;
}
const cookie = parseCookies(req.headers['cookie'])[COOKIE_NAME];
if (cookie && timingSafeEqualStr(cookie, TOKEN)) return true;
return false;
}
function pathnameOf(url) {
const q = url.indexOf('?');
return q >= 0 ? url.slice(0, q) : url;
}
// ========== HTTP Request Handler ==========
function handleRequest(req, res) {
touchActivity();
if (req.method === 'GET' && req.url === '/') {
if (!isAuthorized(req)) {
res.writeHead(403, { 'Content-Type': 'text/html; charset=utf-8' });
res.end(FORBIDDEN_PAGE);
return;
}
// Mirror the key into a cookie so same-origin subresources (/files/*) and the
// WebSocket handshake carry it automatically, whatever URL style the agent
// writes. SameSite=Strict: a cross-site page can neither read the key nor ride
// the cookie; HttpOnly: page scripts can't exfiltrate it.
res.setHeader('Set-Cookie',
COOKIE_NAME + '=' + TOKEN + '; HttpOnly; SameSite=Strict; Path=/');
const pathname = pathnameOf(req.url);
if (req.method === 'GET' && pathname === '/') {
const screenFile = getNewestScreen();
let html = screenFile
? (raw => isFullDocument(raw) ? raw : wrapInFrame(raw))(fs.readFileSync(screenFile, 'utf-8'))
@@ -165,8 +237,8 @@ function handleRequest(req, res) {
res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
res.end(html);
} else if (req.method === 'GET' && req.url.startsWith('/files/')) {
const fileName = path.basename(req.url.slice(7));
} else if (req.method === 'GET' && pathname.startsWith('/files/')) {
const fileName = path.basename(pathname.slice(7));
const filePath = path.join(CONTENT_DIR, fileName);
if (fileName.startsWith('.') || !fs.existsSync(filePath)) {
res.writeHead(404);
@@ -188,6 +260,8 @@ function handleRequest(req, res) {
const clients = new Set();
function handleUpgrade(req, socket) {
if (!isAuthorized(req)) { socket.destroy(); return; }
const key = req.headers['sec-websocket-key'];
if (!key) { socket.destroy(); return; }
@@ -254,7 +328,7 @@ function handleMessage(text) {
}
touchActivity();
console.log(JSON.stringify({ source: 'user-event', ...event }));
if (event.choice) {
if (event && event.choice) {
const eventsFile = path.join(STATE_DIR, 'events');
fs.appendFileSync(eventsFile, JSON.stringify(event) + '\n');
}
@@ -418,7 +492,7 @@ function startServer() {
}
const info = JSON.stringify({
type: 'server-started', port: Number(PORT), host: HOST,
url_host: URL_HOST, url: 'http://' + URL_HOST + ':' + PORT,
url_host: URL_HOST, url: 'http://' + URL_HOST + ':' + PORT + '/?key=' + TOKEN,
screen_dir: CONTENT_DIR, state_dir: STATE_DIR, idle_timeout_ms: IDLE_TIMEOUT_MS
});
console.log(info);

11
skills/brainstorming/visual-companion.md
View File

@@ -37,13 +37,22 @@ The server watches a directory for HTML files and serves the newest one to the b
# the first screen; --project-dir persists mockups and enables same-port restart.
scripts/start-server.sh --project-dir /path/to/project --open
# Returns: {"type":"server-started","port":52341,"url":"http://localhost:52341",
# Returns: {"type":"server-started","port":52341,
# "url":"http://localhost:52341/?key=ab12…",
# "screen_dir":"/path/to/project/.superpowers/brainstorm/12345-1706000000/content",
# "state_dir":"/path/to/project/.superpowers/brainstorm/12345-1706000000/state"}
```
Save `screen_dir` and `state_dir` from the response. With `--open`, the browser opens itself when you push the first screen — you don't need to ask the user to open it, but still share the URL as a fallback (headless/remote setups won't auto-open).
**The URL contains a session key (`?key=…`).** The server rejects any request
without it, so always give the user the **complete** URL from the `url` field —
never strip the query string, and never hand out a bare `http://host:port`. The
key gates HTTP and WebSocket access so a stray browser tab or another machine on
the network can't read the screens or inject events. After the first load the
browser remembers the key via a cookie, so reloads and `/files/*` assets work
without repeating it.
**Finding connection info:** The server writes its startup JSON to `$STATE_DIR/server-info`. If you launched the server in the background and didn't capture stdout, read that file to get the URL and port. When using `--project-dir`, check `<project>/.superpowers/brainstorm/` for the session directory.
**Note:** Pass the project root as `--project-dir` so mockups persist in `.superpowers/brainstorm/` and survive server restarts. Without it, files go to `/tmp` and get cleaned up. Remind the user to add `.superpowers/` to `.gitignore` if it's not already there.

201
tests/brainstorm-server/auth.test.js Normal file
View File

@@ -0,0 +1,201 @@
/**
* Security tests for the brainstorm server's per-session key.
*
* The companion server is reachable by any local browser tab (default loopback
* bind) and by any host that can route to it (remote `--host 0.0.0.0` bind).
* A per-session secret key gates every endpoint so that neither a browser
* confused-deputy nor a direct remote client can read screens/files or inject
* events into state/events (prompt injection into a live agent session).
*
* Auth = a valid `?key=<token>` query param OR a valid session cookie.
*
* Uses the `ws` npm package as a test client (test-only dependency).
*/
const { spawn } = require('child_process');
const http = require('http');
const WebSocket = require('ws');
const fs = require('fs');
const path = require('path');
const assert = require('assert');
const SERVER_PATH = path.join(__dirname, '../../skills/brainstorming/scripts/server.cjs');
const TEST_PORT = 3335;
const TEST_DIR = '/tmp/brainstorm-auth-test';
const CONTENT_DIR = path.join(TEST_DIR, 'content');
const TOKEN = 'testtoken-0123456789abcdef0123456789abcdef';
const COOKIE_NAME = `brainstorm-key-${TEST_PORT}`;
function cleanup() {
if (fs.existsSync(TEST_DIR)) fs.rmSync(TEST_DIR, { recursive: true });
}
async function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
// Raw HTTP GET with optional key query and Cookie header.
function get(pathname, { key, cookie } = {}) {
const url = `http://localhost:${TEST_PORT}${pathname}` + (key !== undefined ? `?key=${key}` : '');
const headers = {};
if (cookie) headers['Cookie'] = cookie;
return new Promise((resolve, reject) => {
http.get(url, { headers }, (res) => {
let data = '';
res.on('data', chunk => data += chunk);
res.on('end', () => resolve({ status: res.statusCode, headers: res.headers, body: data }));
}).on('error', reject);
});
}
// Try to open a WebSocket; resolve 'opened' or 'rejected'.
function wsConnect({ key, cookie } = {}) {
const url = `ws://localhost:${TEST_PORT}/` + (key !== undefined ? `?key=${key}` : '');
const opts = cookie ? { headers: { Cookie: cookie } } : {};
const ws = new WebSocket(url, opts);
return new Promise((resolve) => {
let settled = false;
const done = (outcome) => { if (!settled) { settled = true; resolve({ outcome, ws }); } };
ws.on('open', () => done('opened'));
ws.on('error', () => done('rejected'));
ws.on('close', () => done('rejected'));
setTimeout(() => done('rejected'), 1500);
});
}
function startServer() {
return spawn('node', [SERVER_PATH], {
env: { ...process.env, BRAINSTORM_PORT: TEST_PORT, BRAINSTORM_DIR: TEST_DIR, BRAINSTORM_TOKEN: TOKEN }
});
}
async function waitForServer(server) {
let stdout = '', stderr = '';
return new Promise((resolve, reject) => {
server.stdout.on('data', (d) => {
stdout += d.toString();
if (stdout.includes('server-started')) resolve({ stdout });
});
server.stderr.on('data', (d) => { stderr += d.toString(); });
server.on('error', reject);
setTimeout(() => reject(new Error(`Server didn't start. stderr: ${stderr}`)), 5000);
});
}
async function runTests() {
cleanup();
fs.mkdirSync(CONTENT_DIR, { recursive: true });
fs.writeFileSync(path.join(CONTENT_DIR, 'screen.html'), '<h2>Secret screen</h2>');
fs.writeFileSync(path.join(CONTENT_DIR, 'asset.txt'), 'secret asset');
const server = startServer();
let stdoutAccum = '';
server.stdout.on('data', (d) => { stdoutAccum += d.toString(); });
const { stdout: initialStdout } = await waitForServer(server);
let passed = 0, failed = 0;
async function test(name, fn) {
try { await fn(); console.log(` PASS: ${name}`); passed++; }
catch (e) { console.log(` FAIL: ${name}`); console.log(` ${e.message}`); failed++; }
}
try {
console.log('\n--- Startup URL ---');
await test('server-started url includes the session key', () => {
const msg = JSON.parse(initialStdout.trim());
assert(msg.url.includes(`key=${TOKEN}`), `url should carry the key, got: ${msg.url}`);
});
console.log('\n--- HTTP / gate ---');
await test('GET / without key is rejected with 403', async () => {
const res = await get('/');
assert.strictEqual(res.status, 403, 'no-key request must be 403');
});
await test('403 page names "coding agent" and the key', async () => {
const res = await get('/');
assert(/coding agent/i.test(res.body), '403 body should reference the coding agent');
assert(/key/i.test(res.body), '403 body should mention the key');
});
await test('GET / with wrong key is rejected with 403', async () => {
const res = await get('/', { key: 'wrong-token' });
assert.strictEqual(res.status, 403);
});
await test('GET / with valid key serves the screen', async () => {
const res = await get('/', { key: TOKEN });
assert.strictEqual(res.status, 200);
assert(res.body.includes('Secret screen'), 'should serve the screen content');
});
await test('valid key load sets an HttpOnly SameSite=Strict cookie', async () => {
const res = await get('/', { key: TOKEN });
const setCookie = (res.headers['set-cookie'] || []).join('; ');
assert(setCookie.includes(`${COOKIE_NAME}=${TOKEN}`), `should set ${COOKIE_NAME}`);
assert(/HttpOnly/i.test(setCookie), 'cookie should be HttpOnly');
assert(/SameSite=Strict/i.test(setCookie), 'cookie should be SameSite=Strict');
});
await test('GET / with valid cookie (no query key) serves the screen', async () => {
const res = await get('/', { cookie: `${COOKIE_NAME}=${TOKEN}` });
assert.strictEqual(res.status, 200);
assert(res.body.includes('Secret screen'));
});
console.log('\n--- HTTP /files gate ---');
await test('GET /files without key is rejected with 403', async () => {
const res = await get('/files/asset.txt');
assert.strictEqual(res.status, 403);
});
await test('GET /files with valid key serves the file', async () => {
const res = await get('/files/asset.txt', { key: TOKEN });
assert.strictEqual(res.status, 200);
assert(res.body.includes('secret asset'));
});
console.log('\n--- WebSocket gate ---');
await test('WS upgrade without key is rejected', async () => {
const { outcome, ws } = await wsConnect();
ws.close();
assert.strictEqual(outcome, 'rejected', 'unauthenticated WS must not open');
});
await test('WS upgrade with valid key opens', async () => {
const { outcome, ws } = await wsConnect({ key: TOKEN });
ws.close();
assert.strictEqual(outcome, 'opened');
});
await test('WS upgrade with valid cookie opens', async () => {
const { outcome, ws } = await wsConnect({ cookie: `${COOKIE_NAME}=${TOKEN}` });
ws.close();
assert.strictEqual(outcome, 'opened');
});
console.log('\n--- Robustness (A3) ---');
await test('null payload over an authed WS does not crash the server', async () => {
const { ws } = await wsConnect({ key: TOKEN });
ws.send('null');
await sleep(300);
const res = await get('/', { key: TOKEN });
assert.strictEqual(res.status, 200, 'server must still respond after null payload');
ws.close();
});
console.log(`\n--- Results: ${passed} passed, ${failed} failed ---`);
if (failed > 0) process.exit(1);
} finally {
server.kill();
await sleep(100);
cleanup();
}
}
runTests().catch(err => { console.error('Test failed:', err); process.exit(1); });

2
tests/brainstorm-server/package.json
View File

@@ -2,7 +2,7 @@
"name": "brainstorm-server-tests",
"version": "1.0.0",
"scripts": {
"test": "node ws-protocol.test.js && node helper.test.js && node server.test.js && node lifecycle.test.js && bash stop-server.test.sh"
"test": "node ws-protocol.test.js && node helper.test.js && node auth.test.js && node server.test.js && node lifecycle.test.js && bash stop-server.test.sh"
},
"dependencies": {
"ws": "^8.19.0"

30
tests/brainstorm-server/server.test.js
View File

@@ -20,6 +20,9 @@ const TEST_PORT = 3334;
const TEST_DIR = '/tmp/brainstorm-test';
const CONTENT_DIR = path.join(TEST_DIR, 'content');
const STATE_DIR = path.join(TEST_DIR, 'state');
// Fixed session key so the test client can authenticate (see auth.test.js for
// the security behavior itself; here we just need authorized requests).
const TOKEN = 'testtoken-server-0123456789abcdef';
function cleanup() {
if (fs.existsSync(TEST_DIR)) {
@@ -32,8 +35,9 @@ async function sleep(ms) {
}
async function fetch(url) {
const authed = url + (url.includes('?') ? '&' : '?') + 'key=' + TOKEN;
return new Promise((resolve, reject) => {
http.get(url, (res) => {
http.get(authed, (res) => {
let data = '';
res.on('data', chunk => data += chunk);
res.on('end', () => resolve({
@@ -47,7 +51,7 @@ async function fetch(url) {
function startServer() {
return spawn('node', [SERVER_PATH], {
env: { ...process.env, BRAINSTORM_PORT: TEST_PORT, BRAINSTORM_DIR: TEST_DIR }
env: { ...process.env, BRAINSTORM_PORT: TEST_PORT, BRAINSTORM_DIR: TEST_DIR, BRAINSTORM_TOKEN: TOKEN }
});
}
@@ -207,7 +211,7 @@ async function runTests() {
console.log('\n--- WebSocket Communication ---');
await test('accepts WebSocket upgrade on /', async () => {
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise((resolve, reject) => {
ws.on('open', resolve);
ws.on('error', reject);
@@ -217,7 +221,7 @@ async function runTests() {
await test('relays user events to stdout with source field', async () => {
stdoutAccum = '';
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
ws.send(JSON.stringify({ type: 'click', text: 'Test Button' }));
@@ -233,7 +237,7 @@ async function runTests() {
const eventsFile = path.join(STATE_DIR, 'events');
if (fs.existsSync(eventsFile)) fs.unlinkSync(eventsFile);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
ws.send(JSON.stringify({ type: 'click', choice: 'b', text: 'Option B' }));
@@ -251,7 +255,7 @@ async function runTests() {
const eventsFile = path.join(STATE_DIR, 'events');
if (fs.existsSync(eventsFile)) fs.unlinkSync(eventsFile);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
ws.send(JSON.stringify({ type: 'hover', text: 'Something' }));
@@ -263,8 +267,8 @@ async function runTests() {
});
await test('handles multiple concurrent WebSocket clients', async () => {
const ws1 = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws2 = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws1 = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
const ws2 = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await Promise.all([
new Promise(resolve => ws1.on('open', resolve)),
new Promise(resolve => ws2.on('open', resolve))
@@ -289,7 +293,7 @@ async function runTests() {
});
await test('cleans up closed clients from broadcast list', async () => {
const ws1 = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws1 = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws1.on('open', resolve));
ws1.close();
await sleep(100);
@@ -301,7 +305,7 @@ async function runTests() {
});
await test('handles malformed JSON from client gracefully', async () => {
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
// Send invalid JSON — server should not crash
@@ -318,7 +322,7 @@ async function runTests() {
console.log('\n--- File Watching ---');
await test('sends reload on new .html file', async () => {
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
let gotReload = false;
@@ -338,7 +342,7 @@ async function runTests() {
fs.writeFileSync(filePath, '<h2>Original</h2>');
await sleep(500);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
let gotReload = false;
@@ -354,7 +358,7 @@ async function runTests() {
});
await test('does NOT send reload for non-.html files', async () => {
const ws = new WebSocket(`ws://localhost:${TEST_PORT}`);
const ws = new WebSocket(`ws://localhost:${TEST_PORT}/?key=${TOKEN}`);
await new Promise(resolve => ws.on('open', resolve));
let gotReload = false;