socket.io has an unhandled 'error' event

Overview

Impact

A specially crafted Socket.IO packet can trigger an uncaught exception on the Socket.IO server, thus killing the Node.js process.

node:events:502
    throw err; // Unhandled 'error' event
    ^

Error [ERR_UNHANDLED_ERROR]: Unhandled error. (undefined)
    at new NodeError (node:internal/errors:405:5)
    at Socket.emit (node:events:500:17)
    at /myapp/node_modules/socket.io/lib/socket.js:531:14
    at process.processTicksAndRejections (node:internal/process/task_queues:77:11) {
  code: 'ERR_UNHANDLED_ERROR',
  context: undefined
}

Affected versions

Patches

This issue is fixed by https://github.com/socketio/socket.io/commit/15af22fc22bc6030fcead322c106f07640336115, included in [email protected] (released in May 2023).

The fix was backported in the 2.x branch today: https://github.com/socketio/socket.io/commit/d30630ba10562bf987f4d2b42440fc41a828119c

Workarounds

As a workaround for the affected versions of the socket.io package, you can attach a listener for the "error" event:

io.on("connection", (socket) => {
  socket.on("error", () => {
    // ...
  });
});

For more information

If you have any questions or comments about this advisory:

• Open a discussion here

Thanks a lot to Paul Taylor for the responsible disclosure.

References

• https://github.com/socketio/socket.io/commit/15af22fc22bc6030fcead322c106f07640336115
• https://github.com/socketio/socket.io/commit/d30630ba10562bf987f4d2b42440fc41a828119c

Affected packages

• socket.io >= 3.0.0, < 4.6.2
• socket.io < 2.5.1

Remediation

Upgrade to a patched release:

• socket.io 4.6.2
• socket.io 2.5.1