Description

@grackle-ai/server has Missing WebSocket Origin Header Validation

Impact

The WebSocket upgrade handler in the server validates authentication (API key token or session cookie) but does not check the Origin header. A malicious webpage on a different origin could initiate a WebSocket connection to ws://localhost:3000/ws if it can leverage the user's session cookie (which is SameSite=Lax, allowing top-level navigations).

This enables cross-origin WebSocket hijacking — if a user visits a malicious site while a Grackle session is active, the attacker's page could open a WebSocket and subscribe to real-time events (session output, task updates, environment state).

Affected code:

packages/server/src/ws-bridge.ts:80-91 — connection handler accepts WebSocket upgrades without checking req.headers.origin

Patches

Fix: Validate req.headers.origin against an allowlist before accepting connections:

const origin = req.headers.origin || "";
if (origin && !origin.includes("localhost") && !origin.includes("127.0.0.1")) {
  ws.close(4003, "Invalid origin");
  return;
}

Workarounds

Ensure the Grackle server is only accessible on 127.0.0.1 (the default). Do not use --allow-network in untrusted network environments.

Resources

CWE-346: Origin Validation Error

File: packages/server/src/ws-bridge.ts

Mitigation

Aliases

References