Remote Memory Exposure

Affecting ws package, versions < 1.0.1

medium severity


ws is a simple to use websocket client, server and console for node.js. Affected versions of the package are vulnerable to Uninitialized Memory Exposure.

A client side memory disclosure vulnerability exists in ping functionality of the ws service. When a client sends a ping request and provides an integer value as ping data, it will result in leaking an uninitialized memory buffer.

This is a result of unobstructed use of the Buffer constructor, whose insecure default constructor increases the odds of memory leakage.

ws's ping function uses the default Buffer constructor as-is, making it easy to append uninitialized memory to an existing list. If the value of the buffer list is exposed to users, it may expose raw memory, potentially holding secrets, private data and code.

Proof of Concept:

var ws = require('ws')

var server = new ws.Server({ port: 9000 })
var client = new ws('ws://localhost:9000')

client.on('open', function () {
  console.log('open') // this makes the client allocate an uninitialized buffer of 50 bytes and send it to the server

  client.on('pong', function (data) {
    console.log('got pong')


The Buffer class on Node.js is a mutable array of binary data, and can be initialized with a string, array or number.

const buf1 = new Buffer([1,2,3]);
// creates a buffer containing [01, 02, 03]
const buf2 = new Buffer('test');
// creates a buffer containing ASCII bytes [74, 65, 73, 74]
const buf3 = new Buffer(10);
// creates a buffer of length 10

The first two variants simply create a binary representation of the value it received. The last one, however, pre-allocates a buffer of the specified size, making it a useful buffer, especially when reading data from a stream. When using the number constructor of Buffer, it will allocate the memory, but will not fill it with zeros. Instead, the allocated buffer will hold whatever was in memory at the time. If the buffer is not zeroed by using buf.fill(0), it may leak sensitive information like keys, source code, and system info.

Similar vulnerabilities were discovered in request, mongoose, ws and sequelize.


Snyk patch available for versions:

Do your applications use this vulnerable package?

Feross Aboukhadijeh, Mathias Buss Madsen
Snyk ID
04 Jan, 2016
05 Jan, 2016