WebSocket Abuse: The Silent Threat Lurking in Modern Web Applications

While most security teams are laser focused on HTTP(S) requests, REST APIs, and GraphQL endpoints, there's a quieter but equally powerful protocol often slipping under the radar: WebSockets.

Originally designed for real time communication in web apps, WebSockets are now used extensively in SaaS platforms, online games, stock trading platforms, and collaboration tools like Slack or Trello. But with this speed and bi-directionality comes a new attack surface, one that is often unlogged, unfiltered, and unmonitored by traditional security tools.

In this blog, we’ll demystify WebSockets, break down how attackers are using them to evade detection, walk through a real world abuse case, and provide blue team detection strategies that organizations must adopt before it’s too late.

What Are WebSockets? A Quick Refresher

WebSockets are primarily used for real time, two way communication between a client and a server. Unlike traditional HTTP requests, which are unidirectional and require a new connection for each request, WebSockets maintain a persistent, open connection, enabling continuous, low latency data exchange. This makes them ideal for applications requiring instant updates and interactive experiences. 

WebSockets are a full duplex, bidirectional communication protocol over a single TCP connection. Unlike REST, which relies on the request/response model, WebSockets allow:

• Client and server to communicate continuously

• Minimal overhead once the connection is established

• Real time updates without polling

Main difference between HTTP and WebSockets:

• HTTP: HTTP follows a request-response pattern, creating a new connection for each request. The server doesn't remember your previous interactions.

• Web Sockets: Web Sockets maintain a constant, open connection, allowing the server to recognize and remember you.

Once established, WebSocket traffic is no longer HTTP. It's raw TCP with custom framing, which many proxies, WAFs, and SIEMs fail to inspect.

WebSockets vs HTTP(S)

Why WebSockets Are a Security Blind Spot

Traditional Security Tools Can’t Parse WebSocket Frames

• Many WAFs and IDS systems don’t inspect the payload of WebSocket frames after the initial handshake. Once the connection is upgraded, the security tools may stop logging or inspecting altogether.

Logging Gaps

• Unless explicitly configured, most server logs don’t track what happens within an open WebSocket connection. That’s like leaving the door open and never checking who walks in or out.

Lack of Rate Limiting or Access Control

• WebSocket connections often bypass standard authentication and rate limiting controls that are enforced on HTTP endpoints.

Real World Exploitation: Slack and the "Token Theft via WebSocket" Attack

In 2022, researchers uncovered a serious issue in how Slack (a major collaboration platform) handled WebSocket authentication tokens.

The Attack Flow:

1. Attacker gains access to a shared Slack channel (e.g., via invite).

2. The client connects to Slack's backend using a WebSocket connection.

3. Within the WebSocket payloads, the authentication token was exposed in cleartext.

   1. The attacker can use DevTools or Burp Suite to examine the payloads.

4. This token could be replayed in another browser session, giving full access to the user's Slack workspace, bypassing MFA.

Slack used WebSocket communications to handle real time updates, but didn't properly isolate or encrypt sensitive tokens within those connections.

Blue Team Workflow: Detecting WebSocket Attacks

1. Detect Upgrade headers using proxies (e.g., nginx, HAProxy) or WAF

2. Analyze Frame Contents

   1. Use tools like Zeek or Suricata with custom parsers to inspect the actual payloads of WebSocket frames.

3. Build Sigma Rule for SIEM

   1. You can also create a Sigma rule for monitoring WebSocket abuse from logs that contain WebSocket initiation.

4. Use CSP and WAF Filtering

   1. Block unexpected WebSocket destinations using Content Security Policy (CSP).

   2. Only allow specific origin headers and valid tokens on WebSocket connections.

   
   

Proactive Security Measures for Developers

1. Don’t store or transmit sensitive tokens inside WebSocket payloads.

   1. Use secure HTTP only cookies or OAuth bearer headers in the handshake.

2. Implement WebSocket authentication timeouts

   1. Don’t allow long lived tokens over open connections.

3. Audit WebSocket endpoints regularly using tools like:

   1. Burp Suite

   2. OWASP ZAP (with WebSocket plugin)

4. Log frame contents with caution and obfuscation

The WebSocket protocol is powerful, but with great power comes great responsibility, in this case to secure it. Many organizations don't even realize they have WebSocket endpoints exposed, let alone audit or monitor them.

As an ethical hacker and cybersecurity professional, you must:

• Treat WebSockets as you would any other API

• Demand observability and security parity

• Stay ahead of adversaries who are already exploiting this gap

WebSocket abuse is not theoretical, it's already happening. And unless we give it the security attention it deserves, it will continue to be a silent enabler of breaches.

Stay curious. Stay secure. 🚀

Note: Feel free to drop your thoughts in the comments below, whether it's feedback, a topic you'd love to see covered, or just to say hi! Don’t forget to join the forum for more engaging discussions and stay updated with the latest blog posts. Let’s keep the conversation going and make cybersecurity a community effort!

-AJ