Bobby L. Craig

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

# safe-buffer [![travis][travis-image]][travis-url] [![npm][npm-image]][npm-url] [![downloads][downloads-image]][downloads-url] [![javascript style guide][standard-image]][standard-url] [travis-image]: https://img.shields.io/travis/feross/safe-buffer/master.svg [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 [downloads-image]: https://img.shields.io/npm/dm/safe-buffer.svg [downloads-url]: https://npmjs.org/package/safe-buffer [standard-image]: https://img.shields.io/badge/code_style-standard-brightgreen.svg [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 ``` ## 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) * `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]]) * `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: // changing the TypedArray changes the Buffer also arr[1] = 6000; console.log(buf); // Prints: ``` 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) * `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]) * `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]]) * `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); // ``` 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); // ``` 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); // ``` 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) * `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); // // (octets will be different, every time) buf.fill(0); console.log(buf); // ``` 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) * `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)