safe-buffer/README.md

# safe-buffer [![travis][travis-image]][travis-url] [![npm][npm-image]][npm-url] [![downloads][downloads-image]][downloads-url] [![javascript style guide][standard-image]][standard-url]

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[travis-url]: https://travis-ci.org/feross/safe-buffer
[npm-image]: https://img.shields.io/npm/v/safe-buffer.svg
[npm-url]: https://npmjs.org/package/safe-buffer
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[downloads-url]: https://npmjs.org/package/safe-buffer
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[standard-url]: https://standardjs.com

#### Safer Node.js Buffer API

**Use the new Node.js Buffer APIs (`Buffer.from`, `Buffer.alloc`,
`Buffer.allocUnsafe`, `Buffer.allocUnsafeSlow`) in all versions of Node.js.**

**Uses the built-in implementation when available.**

## install

```
npm install safe-buffer
```

[Get supported safe-buffer with the Tidelift Subscription](https://tidelift.com/subscription/pkg/npm-safe-buffer?utm_source=npm-safe-buffer&utm_medium=referral&utm_campaign=readme)

## usage

The goal of this package is to provide a safe replacement for the node.js `Buffer`.

It's a drop-in replacement for `Buffer`. You can use it by adding one `require` line to
the top of your node.js modules:

```js
var Buffer = require('safe-buffer').Buffer

// Existing buffer code will continue to work without issues:

new Buffer('hey', 'utf8')
new Buffer([1, 2, 3], 'utf8')
new Buffer(obj)
new Buffer(16) // create an uninitialized buffer (potentially unsafe)

// But you can use these new explicit APIs to make clear what you want:

Buffer.from('hey', 'utf8') // convert from many types to a Buffer
Buffer.alloc(16) // create a zero-filled buffer (safe)
Buffer.allocUnsafe(16) // create an uninitialized buffer (potentially unsafe)
```

## api

### Class Method: Buffer.from(array)
<!-- YAML
added: v3.0.0
-->

* `array` {Array}

Allocates a new `Buffer` using an `array` of octets.

```js
const buf = Buffer.from([0x62,0x75,0x66,0x66,0x65,0x72]);
  // creates a new Buffer containing ASCII bytes
  // ['b','u','f','f','e','r']
```

A `TypeError` will be thrown if `array` is not an `Array`.

### Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
<!-- YAML
added: v5.10.0
-->

* `arrayBuffer` {ArrayBuffer} The `.buffer` property of a `TypedArray` or
  a `new ArrayBuffer()`
* `byteOffset` {Number} Default: `0`
* `length` {Number} Default: `arrayBuffer.length - byteOffset`

When passed a reference to the `.buffer` property of a `TypedArray` instance,
the newly created `Buffer` will share the same allocated memory as the
TypedArray.

```js
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;

const buf = Buffer.from(arr.buffer); // shares the memory with arr;

console.log(buf);
  // Prints: <Buffer 88 13 a0 0f>

// changing the TypedArray changes the Buffer also
arr[1] = 6000;

console.log(buf);
  // Prints: <Buffer 88 13 70 17>
```

The optional `byteOffset` and `length` arguments specify a memory range within
the `arrayBuffer` that will be shared by the `Buffer`.

```js
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
console.log(buf.length);
  // Prints: 2
```

A `TypeError` will be thrown if `arrayBuffer` is not an `ArrayBuffer`.

### Class Method: Buffer.from(buffer)
<!-- YAML
added: v3.0.0
-->

* `buffer` {Buffer}

Copies the passed `buffer` data onto a new `Buffer` instance.

```js
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);

buf1[0] = 0x61;
console.log(buf1.toString());
  // 'auffer'
console.log(buf2.toString());
  // 'buffer' (copy is not changed)
```

A `TypeError` will be thrown if `buffer` is not a `Buffer`.

### Class Method: Buffer.from(str[, encoding])
<!-- YAML
added: v5.10.0
-->

* `str` {String} String to encode.
* `encoding` {String} Encoding to use, Default: `'utf8'`

Creates a new `Buffer` containing the given JavaScript string `str`. If
provided, the `encoding` parameter identifies the character encoding.
If not provided, `encoding` defaults to `'utf8'`.

```js
const buf1 = Buffer.from('this is a tést');
console.log(buf1.toString());
  // prints: this is a tést
console.log(buf1.toString('ascii'));
  // prints: this is a tC)st

const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
console.log(buf2.toString());
  // prints: this is a tést
```

A `TypeError` will be thrown if `str` is not a string.

### Class Method: Buffer.alloc(size[, fill[, encoding]])
<!-- YAML
added: v5.10.0
-->

* `size` {Number}
* `fill` {Value} Default: `undefined`
* `encoding` {String} Default: `utf8`

Allocates a new `Buffer` of `size` bytes. If `fill` is `undefined`, the
`Buffer` will be *zero-filled*.

```js
const buf = Buffer.alloc(5);
console.log(buf);
  // <Buffer 00 00 00 00 00>
```

The `size` must be less than or equal to the value of
`require('buffer').kMaxLength` (on 64-bit architectures, `kMaxLength` is
`(2^31)-1`). Otherwise, a [`RangeError`][] is thrown. A zero-length Buffer will
be created if a `size` less than or equal to 0 is specified.

If `fill` is specified, the allocated `Buffer` will be initialized by calling
`buf.fill(fill)`. See [`buf.fill()`][] for more information.

```js
const buf = Buffer.alloc(5, 'a');
console.log(buf);
  // <Buffer 61 61 61 61 61>
```

If both `fill` and `encoding` are specified, the allocated `Buffer` will be
initialized by calling `buf.fill(fill, encoding)`. For example:

```js
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
console.log(buf);
  // <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
```

Calling `Buffer.alloc(size)` can be significantly slower than the alternative
`Buffer.allocUnsafe(size)` but ensures that the newly created `Buffer` instance
contents will *never contain sensitive data*.

A `TypeError` will be thrown if `size` is not a number.

### Class Method: Buffer.allocUnsafe(size)
<!-- YAML
added: v5.10.0
-->

* `size` {Number}

Allocates a new *non-zero-filled* `Buffer` of `size` bytes.  The `size` must
be less than or equal to the value of `require('buffer').kMaxLength` (on 64-bit
architectures, `kMaxLength` is `(2^31)-1`). Otherwise, a [`RangeError`][] is
thrown. A zero-length Buffer will be created if a `size` less than or equal to
0 is specified.

The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`buf.fill(0)`][] to initialize such
`Buffer` instances to zeroes.

```js
const buf = Buffer.allocUnsafe(5);
console.log(buf);
  // <Buffer 78 e0 82 02 01>
  // (octets will be different, every time)
buf.fill(0);
console.log(buf);
  // <Buffer 00 00 00 00 00>
```

A `TypeError` will be thrown if `size` is not a number.

Note that the `Buffer` module pre-allocates an internal `Buffer` instance of
size `Buffer.poolSize` that is used as a pool for the fast allocation of new
`Buffer` instances created using `Buffer.allocUnsafe(size)` (and the deprecated
`new Buffer(size)` constructor) only when `size` is less than or equal to
`Buffer.poolSize >> 1` (floor of `Buffer.poolSize` divided by two). The default
value of `Buffer.poolSize` is `8192` but can be modified.

Use of this pre-allocated internal memory pool is a key difference between
calling `Buffer.alloc(size, fill)` vs. `Buffer.allocUnsafe(size).fill(fill)`.
Specifically, `Buffer.alloc(size, fill)` will *never* use the internal Buffer
pool, while `Buffer.allocUnsafe(size).fill(fill)` *will* use the internal
Buffer pool if `size` is less than or equal to half `Buffer.poolSize`. The
difference is subtle but can be important when an application requires the
additional performance that `Buffer.allocUnsafe(size)` provides.

### Class Method: Buffer.allocUnsafeSlow(size)
<!-- YAML
added: v5.10.0
-->

* `size` {Number}

Allocates a new *non-zero-filled* and non-pooled `Buffer` of `size` bytes.  The
`size` must be less than or equal to the value of
`require('buffer').kMaxLength` (on 64-bit architectures, `kMaxLength` is
`(2^31)-1`). Otherwise, a [`RangeError`][] is thrown. A zero-length Buffer will
be created if a `size` less than or equal to 0 is specified.

The underlying memory for `Buffer` instances created in this way is *not
initialized*. The contents of the newly created `Buffer` are unknown and
*may contain sensitive data*. Use [`buf.fill(0)`][] to initialize such
`Buffer` instances to zeroes.

When using `Buffer.allocUnsafe()` to allocate new `Buffer` instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
`Buffer`. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffers. This approach improves both
performance and memory usage by eliminating the need to track and cleanup as
many `Persistent` objects.

However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer instance using `Buffer.allocUnsafeSlow()` then
copy out the relevant bits.

```js
// need to keep around a few small chunks of memory
const store = [];

socket.on('readable', () => {
  const data = socket.read();
  // allocate for retained data
  const sb = Buffer.allocUnsafeSlow(10);
  // copy the data into the new allocation
  data.copy(sb, 0, 0, 10);
  store.push(sb);
});
```

Use of `Buffer.allocUnsafeSlow()` should be used only as a last resort *after*
a developer has observed undue memory retention in their applications.

A `TypeError` will be thrown if `size` is not a number.

### All the Rest

The rest of the `Buffer` API is exactly the same as in node.js.
[See the docs](https://nodejs.org/api/buffer.html).


## Related links

- [Node.js issue: Buffer(number) is unsafe](https://github.com/nodejs/node/issues/4660)
- [Node.js Enhancement Proposal: Buffer.from/Buffer.alloc/Buffer.zalloc/Buffer() soft-deprecate](https://github.com/nodejs/node-eps/pull/4)

## Why is `Buffer` unsafe?

Today, the node.js `Buffer` constructor is overloaded to handle many different argument
types like `String`, `Array`, `Object`, `TypedArrayView` (`Uint8Array`, etc.),
`ArrayBuffer`, and also `Number`.

The API is optimized for convenience: you can throw any type at it, and it will try to do
what you want.

Because the Buffer constructor is so powerful, you often see code like this:

```js
// Convert UTF-8 strings to hex
function toHex (str) {
  return new Buffer(str).toString('hex')
}
```

***But what happens if `toHex` is called with a `Number` argument?***

### Remote Memory Disclosure

If an attacker can make your program call the `Buffer` constructor with a `Number`
argument, then they can make it allocate uninitialized memory from the node.js process.
This could potentially disclose TLS private keys, user data, or database passwords.

When the `Buffer` constructor is passed a `Number` argument, it returns an
**UNINITIALIZED** block of memory of the specified `size`. When you create a `Buffer` like
this, you **MUST** overwrite the contents before returning it to the user.

From the [node.js docs](https://nodejs.org/api/buffer.html#buffer_new_buffer_size):

> `new Buffer(size)`
>
> - `size` Number
>
> The underlying memory for `Buffer` instances created in this way is not initialized.
> **The contents of a newly created `Buffer` are unknown and could contain sensitive
> data.** Use `buf.fill(0)` to initialize a Buffer to zeroes.

(Emphasis our own.)

Whenever the programmer intended to create an uninitialized `Buffer` you often see code
like this:

```js
var buf = new Buffer(16)

// Immediately overwrite the uninitialized buffer with data from another buffer
for (var i = 0; i < buf.length; i++) {
  buf[i] = otherBuf[i]
}
```


### Would this ever be a problem in real code?

Yes. It's surprisingly common to forget to check the type of your variables in a
dynamically-typed language like JavaScript.

Usually the consequences of assuming the wrong type is that your program crashes with an
uncaught exception. But the failure mode for forgetting to check the type of arguments to
the `Buffer` constructor is more catastrophic.

Here's an example of a vulnerable service that takes a JSON payload and converts it to
hex:

```js
// Take a JSON payload {str: "some string"} and convert it to hex
var server = http.createServer(function (req, res) {
  var data = ''
  req.setEncoding('utf8')
  req.on('data', function (chunk) {
    data += chunk
  })
  req.on('end', function () {
    var body = JSON.parse(data)
    res.end(new Buffer(body.str).toString('hex'))
  })
})

server.listen(8080)
```

In this example, an http client just has to send:

```json
{
  "str": 1000
}
```

and it will get back 1,000 bytes of uninitialized memory from the server.

This is a very serious bug. It's similar in severity to the
[the Heartbleed bug](http://heartbleed.com/) that allowed disclosure of OpenSSL process
memory by remote attackers.


### Which real-world packages were vulnerable?

#### [`bittorrent-dht`](https://www.npmjs.com/package/bittorrent-dht)

[Mathias Buus](https://github.com/mafintosh) and I
([Feross Aboukhadijeh](http://feross.org/)) found this issue in one of our own packages,
[`bittorrent-dht`](https://www.npmjs.com/package/bittorrent-dht). The bug would allow
anyone on the internet to send a series of messages to a user of `bittorrent-dht` and get
them to reveal 20 bytes at a time of uninitialized memory from the node.js process.

Here's
[the commit](https://github.com/feross/bittorrent-dht/commit/6c7da04025d5633699800a99ec3fbadf70ad35b8)
that fixed it. We released a new fixed version, created a
[Node Security Project disclosure](https://nodesecurity.io/advisories/68), and deprecated all
vulnerable versions on npm so users will get a warning to upgrade to a newer version.

#### [`ws`](https://www.npmjs.com/package/ws)

That got us wondering if there were other vulnerable packages. Sure enough, within a short
period of time, we found the same issue in [`ws`](https://www.npmjs.com/package/ws), the
most popular WebSocket implementation in node.js.

If certain APIs were called with `Number` parameters instead of `String` or `Buffer` as
expected, then uninitialized server memory would be disclosed to the remote peer.

These were the vulnerable methods:

```js
socket.send(number)
socket.ping(number)
socket.pong(number)
```

Here's a vulnerable socket server with some echo functionality:

```js
server.on('connection', function (socket) {
  socket.on('message', function (message) {
    message = JSON.parse(message)
    if (message.type === 'echo') {
      socket.send(message.data) // send back the user's message
    }
  })
})
```

`socket.send(number)` called on the server, will disclose server memory.

Here's [the release](https://github.com/websockets/ws/releases/tag/1.0.1) where the issue
was fixed, with a more detailed explanation. Props to
[Arnout Kazemier](https://github.com/3rd-Eden) for the quick fix. Here's the
[Node Security Project disclosure](https://nodesecurity.io/advisories/67).


### What's the solution?

It's important that node.js offers a fast way to get memory otherwise performance-critical
applications would needlessly get a lot slower.

But we need a better way to *signal our intent* as programmers. **When we want
uninitialized memory, we should request it explicitly.**

Sensitive functionality should not be packed into a developer-friendly API that loosely
accepts many different types. This type of API encourages the lazy practice of passing
variables in without checking the type very carefully.

#### A new API: `Buffer.allocUnsafe(number)`

The functionality of creating buffers with uninitialized memory should be part of another
API. We propose `Buffer.allocUnsafe(number)`. This way, it's not part of an API that
frequently gets user input of all sorts of different types passed into it.

```js
var buf = Buffer.allocUnsafe(16) // careful, uninitialized memory!

// Immediately overwrite the uninitialized buffer with data from another buffer
for (var i = 0; i < buf.length; i++) {
  buf[i] = otherBuf[i]
}
```


### How do we fix node.js core?

We sent [a PR to node.js core](https://github.com/nodejs/node/pull/4514) (merged as
`semver-major`) which defends against one case:

```js
var str = 16
new Buffer(str, 'utf8')
```

In this situation, it's implied that the programmer intended the first argument to be a
string, since they passed an encoding as a second argument. Today, node.js will allocate
uninitialized memory in the case of `new Buffer(number, encoding)`, which is probably not
what the programmer intended.

But this is only a partial solution, since if the programmer does `new Buffer(variable)`
(without an `encoding` parameter) there's no way to know what they intended. If `variable`
is sometimes a number, then uninitialized memory will sometimes be returned.

### What's the real long-term fix?

We could deprecate and remove `new Buffer(number)` and use `Buffer.allocUnsafe(number)` when
we need uninitialized memory. But that would break 1000s of packages.

~~We believe the best solution is to:~~

~~1. Change `new Buffer(number)` to return safe, zeroed-out memory~~

~~2. Create a new API for creating uninitialized Buffers. We propose: `Buffer.allocUnsafe(number)`~~

#### Update

We now support adding three new APIs:

- `Buffer.from(value)` - convert from any type to a buffer
- `Buffer.alloc(size)` - create a zero-filled buffer
- `Buffer.allocUnsafe(size)` - create an uninitialized buffer with given size

This solves the core problem that affected `ws` and `bittorrent-dht` which is
`Buffer(variable)` getting tricked into taking a number argument.

This way, existing code continues working and the impact on the npm ecosystem will be
minimal. Over time, npm maintainers can migrate performance-critical code to use
`Buffer.allocUnsafe(number)` instead of `new Buffer(number)`.


### Conclusion

We think there's a serious design issue with the `Buffer` API as it exists today. It
promotes insecure software by putting high-risk functionality into a convenient API
with friendly "developer ergonomics".

This wasn't merely a theoretical exercise because we found the issue in some of the
most popular npm packages.

Fortunately, there's an easy fix that can be applied today. Use `safe-buffer` in place of
`buffer`.

```js
var Buffer = require('safe-buffer').Buffer
```

Eventually, we hope that node.js core can switch to this new, safer behavior. We believe
the impact on the ecosystem would be minimal since it's not a breaking change.
Well-maintained, popular packages would be updated to use `Buffer.alloc` quickly, while
older, insecure packages would magically become safe from this attack vector.


## links

- [Node.js PR: buffer: throw if both length and enc are passed](https://github.com/nodejs/node/pull/4514)
- [Node Security Project disclosure for `ws`](https://nodesecurity.io/advisories/67)
- [Node Security Project disclosure for`bittorrent-dht`](https://nodesecurity.io/advisories/68)


## credit

The original issues in `bittorrent-dht`
([disclosure](https://nodesecurity.io/advisories/68)) and
`ws` ([disclosure](https://nodesecurity.io/advisories/67)) were discovered by
[Mathias Buus](https://github.com/mafintosh) and
[Feross Aboukhadijeh](http://feross.org/).

Thanks to [Adam Baldwin](https://github.com/evilpacket) for helping disclose these issues
and for his work running the [Node Security Project](https://nodesecurity.io/).

Thanks to [John Hiesey](https://github.com/jhiesey) for proofreading this README and
auditing the code.


## license

MIT. Copyright (C) [Feross Aboukhadijeh](http://feross.org)