WebSocket security best practices and checklist

What is WebSocket?

WebSocket is a communication protocol that provides full-duplex, persistent connections between clients and servers over a single TCP connection. Unlike traditional HTTP, which follows a request-response model, WebSocket (specified in RFC 6455) enables real-time, two-way interaction, making it the go-to solution for applications such as chat services, live updates, online gaming, and collaborative tools. The protocol begins with an HTTP handshake and then upgrades the connection, allowing messages to flow asynchronously in both directions.

Why is WebSocket security important?

WebSockets remove much of the overhead associated with HTTP polling and enable faster, more interactive user experiences—but that speed and flexibility come with unique security risks. Because WebSocket connections stay open, they present a larger attack window. Additionally, their deviation from the conventional request-response model means traditional security controls such as WAFs and proxies may offer limited protection. Without rigorous input validation and session handling, WebSocket endpoints can be exploited to bypass authentication, exfiltrate data, or carry out injection attacks.

Common WebSocket security vulnerabilities

Several classes of security weaknesses can result in vulnerabilities in applications that use WebSockets:

• Lack of encryption (using ws:// instead of wss://)
• Improper client input validation, allowing for injection attacks
• Failure to validate server data, risking logic flaws or client-side compromise
• Insecure authentication or session management
• Absence of origin checks, exposing endpoints to cross-site WebSocket hijacking
• Tunneling sensitive data through WebSocket improperly, leading to leakage or protocol abuse

WebSocket security best practices

Use WSS (WebSocket over TLS)

Always encrypt WebSocket traffic with wss://. This ensures confidentiality and integrity of the data in transit, preventing eavesdropping and man-in-the-middle (MITM) attacks. Using wss:// also enables browser-based security features such as mixed content blocking and strict transport security.

Avoid tunneling sensitive protocols or data

Don’t use WebSocket to tunnel HTTP or other protocols carrying sensitive data unless absolutely necessary and adequately secured. Tunneling can bypass standard security controls and introduce unintended attack vectors. If tunneling is unavoidable, implement strict input validation and monitoring to detect misuse.

Validate client input

All input received over a WebSocket connection should be treated as untrusted. Implement server-side validation and sanitation routines to prevent injection attacks and business logic abuse. Consider using schema validation for structured payloads like JSON to enforce expected formats.

Validate server data before processing

Just as clients must be treated as untrusted, client-side applications should also validate data received from the server to mitigate the impact of server-side bugs or data manipulation. This helps prevent corrupted or malicious data from affecting the client’s behavior or UI.

Enforce authentication and authorization

Ensure WebSocket connections are initiated only by authenticated users. Authorization checks must be applied per message or action, not just at the handshake stage. Token-based authentication tied to the initial HTTP upgrade request can help enforce this. Additionally, tokens should be short-lived and scoped to reduce the impact of compromise.

Check the Origin header

During the initial WebSocket handshake, validate the Origin header to ensure the request is coming from an expected and trusted source. This helps protect against cross-site WebSocket hijacking attacks. Always compare the Origin to an allowlist of trusted domains and reject requests from unverified sources. Note that the Origin header can be absent or spoofed in non-browser clients, so it should be used in combination with authentication controls.

How Invicti can help with WebSocket security

Invicti helps organizations maintain a strong security posture across all exposed web application interfaces, including those that use WebSockets. While WebSocket endpoints are less common than REST or GraphQL APIs, they can still be crawled, discovered, and tested as part of a broader dynamic application security testing (DAST) process.

With Invicti, security teams benefit from:

• Automatic discovery of exposed WebSocket endpoints during crawling
• Robust scanning for vulnerabilities in WebSocket handlers, including input validation and authentication issues
• Authenticated scanning workflows that mimic real user sessions, allowing accurate testing of secured WebSocket connections
• Actionable, verified results through Invicti’s proof-based scanning, reducing false positives and enabling fast, confident remediation

By integrating Invicti into your CI/CD pipeline and adopting a DAST-first approach, you can continuously assess the security of both traditional web apps and newer real-time features like WebSockets, ensuring no endpoint goes unchecked.

FAQs: WebSocket security