Cube.js Crash Course: Async Nightmares and WebSocket Woes

If you've ever built a dashboard, you know the pain of translating raw SQL into something a frontend developer can actually use. Enter Cube (formerly Cube.js). It sits between your database and your frontend, acting as a 'semantic layer' that handles caching, access control, and query generation. It is the brain of your data infrastructure.

But here is the problem with brains: they are fragile. In the world of Node.js, a single unhandled error is enough to lobotomize the entire application. CVE-2026-25957 isn't some complex buffer overflow involving ROP chains; it is a lesson in why modern JavaScript error handling is non-negotiable.

This vulnerability is a 'pick your poison' situation. Do you want to crash the server instantly by exploiting unawaited promises? Do you want to hang the CPU with a Regular Expression Denial of Service (ReDoS) via the date parser? or do you want to explode the memory usage via WebSocket pollution? Cube offered all three on a silver platter.

The primary vector here is a fundamental misunderstanding of the Node.js event loop. In older versions of Node, an UnhandledPromiseRejection was just a warning. The runtime would nag you, but keep chugging along. In modern Node.js (v15+), an unhandled rejection is fatal. It kills the process immediately.

Cube's API Gateway had several endpoints—specifically /v1/load, /v1/sql, and /v1/meta—that treated response logic as 'fire and forget.' The developers invoked the response handling functions (sending JSON to the client) without the await keyword.

Why does this matter? If the network connection is unstable—or if an attacker intentionally makes it unstable by sending a TCP RST packet mid-response—the write operation fails. The promise rejects. Because the code didn't await the operation within a try/catch block, that rejection bubbles up to the global scope. The Node process panics and terminates. It is like pulling the pin on a grenade and then walking away without checking if you actually threw it.

Secondary to this suicide-by-async, the WebSocket implementation in LocalSubscriptionStore used plain JavaScript objects ({}) to store subscriptions. This is JavaScript 101: never use {} as a hash map for user-controlled keys. It opens the door to prototype pollution and makes iteration computationally expensive if an attacker floods the system with keys.

Let's look at the anatomy of the failure. The vulnerable code in the API Gateway looked something like this (simplified for clarity):

// Vulnerable Pattern in API Gateway
app.get('/v1/load', (req, res) => {
  // ... processing query ...
  
  // DANGER: No await, no catch.
  // If this promise rejects (e.g., socket closed), the process crashes.
  this.apiGateway.load(req.query).then(result => {
    res.json(result);
  });
});

If res.json(result) fails—which can happen if the client disconnects before the payload is flushed—the promise chain breaks. Since there is no .catch() attached to that specific chain or an encompassing await inside a try/catch, the error goes unhandled.

The fix introduced in version 1.5.13 wraps these boundaries strictly:

// Patched Pattern
app.get('/v1/load', async (req, res) => {
  try {
    const result = await this.apiGateway.load(req.query);
    res.json(result);
  } catch (e) {
    // Ideally handle specific errors, but at least don't crash.
    if (!res.headersSent) {
      res.status(500).json({ error: e.message });
    }
  }
});

Additionally, the WebSocket storage was refactored. They moved from this.subscriptions = {} to this.subscriptions = new Map(). This prevents key collisions with Object.prototype methods and generally improves performance during high-concurrency scenarios.

Exploiting this requires low-level authentication (Standard User), but the impact is high availability loss. We can execute a "Ghost Disconnect" attack.

Step 1: Authentication

Obtain a valid JWT or API token. Since Cube is often exposed to frontend clients, these tokens are frequently accessible in browser local storage or network traffic.

Step 2: The Setup

We craft a legitimate, heavy query to the /v1/load endpoint. We want the server to spend a few milliseconds processing so we have a window of opportunity.

GET /cubejs-api/v1/load?query={...heavy_aggregation...} HTTP/1.1
Host: target-cube.io
Authorization: Bearer <token>

Step 3: The Execution

We send the request, wait for the server to acknowledge, and immediately send a TCP RST (Reset) packet or simply close the socket from the client side before the server can flush the response buffer.

# Conceptual PoC logic
(echo -e "GET /v1/load...\r\n"; sleep 0.1) | nc target 4000
# The 'nc' process closing creates a Broken Pipe on the server.

The Result

The server attempts to write to the closed socket. The stream throws an error. The promise rejects. The Node.js process prints ERR_UNHANDLED_REJECTION and exits with status code 1. Kubernetes might restart the pod, but a script doing this 10 times a second keeps the service permanently offline.

This is a Denial of Service (DoS), which some security teams dismiss as 'boring.' Do not be one of those teams. Cube typically powers analytics dashboards for C-suite executives or customer-facing reporting tools.

When Cube goes down, the CEO's dashboard goes blank. When the CEO's dashboard goes blank, the CISO's phone starts ringing.

Furthermore, because the vulnerability involves the event loop and memory consumption (via the secondary WebSocket and ReDoS vectors), an attacker could degrade performance subtly rather than crashing it outright. This leads to increased cloud bills (if autoscaling kicks in to handle the 'load') and frustrating user experiences that are harder to debug than a clean crash.

The remediation is straightforward: Update Cube.js.

Vendors released versions 1.5.13 and 1.4.2 to address these issues. The patch notes read like a confession of technical debt repayment:

1. Async Boundaries: All API handlers now properly await results.
2. Input Validation: Zod schemas were introduced to validate WebSocket messages strictly.
3. Data Structures: Map replaced plain objects for subscription storage.
4. ReDoS Protection: chrono-node usage now includes length limits on date strings.

If you cannot upgrade immediately (why?), you can mitigate the WebSocket vector by setting the environment variable CUBEJS_WEB_SOCKETS=false if your app doesn't use real-time features. However, the async crash vector in the REST API remains until the code is patched.