Version Details and Security Vulnerabilities

The socket.io-parser npm package before versions 3.3.2 and 3.4.1 allows attackers to cause a denial of service (memory consumption) via a large packet because a concatenation approach is used.

Due to improper type validation in the socket.io-parser library (which is used by the socket.io and socket.io-client packages to encode and decode Socket.IO packets), it is possible to overwrite the _placeholder object which allows an attacker to place references to functions at arbitrary places in the resulting query object.

Example:

const decoder = new Decoder();

decoder.on("decoded", (packet) => {
 console.log(packet.data); // prints [ 'hello', [Function: splice] ]
})

decoder.add('51-["hello",{"_placeholder":true,"num":"splice"}]');
decoder.add(Buffer.from("world"));

This bubbles up in the socket.io package:

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 // here, "val" could be a function instead of a buffer
 });
});

:warning: IMPORTANT NOTE :warning:

You need to make sure that the payload that you received from the client is actually a Buffer object:

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 if (!Buffer.isBuffer(val)) {
 socket.disconnect();
 return;
 }
 // ...
 });
});

If that's already the case, then you are not impacted by this issue, and there is no way an attacker could make your server crash (or escalate privileges, ...).

Example of values that could be sent by a malicious user:

• a number that is out of bounds

Sample packet: 451-["hello",{"_placeholder":true,"num":10}]

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 // val is `undefined`
 });
});

• a value that is not a number, like undefined

Sample packet: 451-["hello",{"_placeholder":true,"num":undefined}]

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 // val is `undefined`
 });
});

• a string that is part of the prototype of Array, like "push"

Sample packet: 451-["hello",{"_placeholder":true,"num":"push"}]

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 // val is a reference to the "push" function
 });
});

• a string that is part of the prototype of Object, like "hasOwnProperty"

Sample packet: 451-["hello",{"_placeholder":true,"num":"hasOwnProperty"}]

io.on("connection", (socket) => {
 socket.on("hello", (val) => {
 // val is a reference to the "hasOwnProperty" function
 });
});

This should be fixed by:

• https://github.com/socketio/socket.io-parser/commit/b5d0cb7dc56a0601a09b056beaeeb0e43b160050, included in socket.io-parser@4.2.1
• https://github.com/socketio/socket.io-parser/commit/b559f050ee02bd90bd853b9823f8de7fa94a80d4, included in socket.io-parser@4.0.5
• https://github.com/socketio/socket.io-parser/commit/04d23cecafe1b859fb03e0cbf6ba3b74dff56d14, included in socket.io-parser@3.4.2
• https://github.com/socketio/socket.io-parser/commit/fb21e422fc193b34347395a33e0f625bebc09983, included in socket.io-parser@3.3.3

Dependency analysis for the socket.io package

| socket.io version | socket.io-parser version | Covered? | |---------------------|---------------------------------------------------------------------------------------------------------|------------------------| | 4.5.2...latest | ~4.2.0 (ref) | Yes :heavy_check_mark: | | 4.1.3...4.5.1 | ~4.0.4 (ref) | Yes :heavy_check_mark: | | 3.0.5...4.1.2 | ~4.0.3 (ref) | Yes :heavy_check_mark: | | 3.0.0...3.0.4 | ~4.0.1 (ref) | Yes :heavy_check_mark: | | 2.3.0...2.5.0 | ~3.4.0 (ref) | Yes :heavy_check_mark: |

Dependency analysis for the socket.io-client package

| socket.io-client version | socket.io-parser version | Covered? | |----------------------------|----------------------------------------------------------------------------------------------------------------|------------------------------------| | 4.5.0...latest | ~4.2.0 (ref) | Yes :heavy_check_mark: | | 4.3.0...4.4.1 | ~4.1.1 (ref) | No, but the impact is very limited | | 3.1.0...4.2.0 | ~4.0.4 (ref) | Yes :heavy_check_mark: | | 3.0.5 | ~4.0.3 (ref) | Yes :heavy_check_mark: | | 3.0.0...3.0.4 | ~4.0.1 (ref) | Yes :heavy_check_mark: | | 2.2.0...2.5.0 | ~3.3.0 (ref) | Yes :heavy_check_mark: |

Impact

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

TypeError: Cannot convert object to primitive value
       at Socket.emit (node:events:507:25)
       at .../node_modules/socket.io/lib/socket.js:531:14

Patches

A fix has been released today (2023/05/22):

• https://github.com/socketio/socket.io-parser/commit/3b78117bf6ba7e99d7a5cfc1ba54d0477554a7f3, included in socket.io-parser@4.2.3
• https://github.com/socketio/socket.io-parser/commit/2dc3c92622dad113b8676be06f23b1ed46b02ced, included in socket.io-parser@3.4.3

Another fix has been released for the 3.3.x branch:

• https://github.com/socketio/socket.io-parser/commit/ee006607495eca4ec7262ad080dd3a91439a5ba4, included in `socket.io-parser@3.3.4

| socket.io version | socket.io-parser version | Needs minor update? | |---------------------|---------------------------------------------------------------------------------------------------------|--------------------------------------| | 4.5.2...latest | ~4.2.0 (ref) | npm audit fix should be sufficient | | 4.1.3...4.5.1 | ~4.1.1 (ref) | Please upgrade to socket.io@4.6.x | | 3.0.5...4.1.2 | ~4.0.3 (ref) | Please upgrade to socket.io@4.6.x | | 3.0.0...3.0.4 | ~4.0.1 (ref) | Please upgrade to socket.io@4.6.x | | 2.3.0...2.5.0 | ~3.4.0 (ref) | npm audit fix should be sufficient |

Workarounds

There is no known workaround except upgrading to a safe version.

For more information

If you have any questions or comments about this advisory:

• Open a discussion here

Thanks to @rafax00 for the responsible disclosure.