CWE-603: Use of Client-Side Authentication

What is Use of Client-Side Authentication?

• Overview: CWE-603 refers to the practice of performing authentication only on the client side, without validating on the server side. This can lead to security breaches if a client application is modified to bypass authentication checks.

• Exploitation Methods:

• Attackers can exploit this vulnerability by intercepting and modifying client-side code or communications to bypass authentication.
• Common attack patterns include using tools to decompile or reverse-engineer the client application, modifying the client to skip authentication steps, and directly communicating with the server using unauthorized requests.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to restricted application features or data.
• Potential cascading effects include data breaches, privilege escalation, and further exploitation of sensitive operations or information.
• Business impact can be significant, leading to data loss, reputational damage, and financial losses due to compromised assets and potential regulatory penalties.

• Prevention Guidelines:

• Specific code-level fixes include implementing and enforcing all authentication checks server-side, ensuring the server independently verifies credentials.
• Security best practices involve treating client-side operations as untrusted, routinely updating security measures on both client and server sides, and employing encryption for data in transit.
• Recommended tools and frameworks include using well-established libraries for authentication and encryption, leveraging secure communication protocols like HTTPS, and conducting regular security audits and penetration testing to identify and rectify vulnerabilities.

Corgea can automatically detect and fix Use of Client-Side Authentication in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: ICS/OT

Vulnerable Code Example

JavaScript Example

// Vulnerable code: Authentication is handled on the client-side, which can be easily bypassed
function authenticateUser(token) {
    // This hardcoded token check is insecure as it can be easily bypassed or manipulated
    if (token === "valid-user-token") {
        // Grant access to the user
        console.log("Access granted.");
        return true;
    } else {
        // Deny access
        console.log("Access denied.");
        return false;
    }
}

// The server relies on the client to authenticate, which is insecure
const userToken = "valid-user-token"; // This should come from client-side input
authenticateUser(userToken); // Authentication logic is executed on the client-side

Explanation of the Vulnerability

• Client-Side Authentication: The authentication logic is executed entirely on the client-side, allowing an attacker to modify the code and bypass authentication.
• Hardcoded Tokens: Using hardcoded tokens for authentication is insecure because attackers can easily discover and exploit them.
• Insecure Trust: The server trusts the client to authenticate itself, which is inherently insecure as clients can be tampered with.

How to fix Use of Client-Side Authentication?

Fixed Code Example

JavaScript Example

// Secure code: Authentication is handled on the server-side
const express = require('express');
const app = express();
const validTokens = ['valid-user-token']; // Example of a secure token store

app.use(express.json());

app.post('/authenticate', (req, res) => {
    const { token } = req.body; // Token sent by client within the request body

    // Authentication logic is performed on the server-side
    if (validTokens.includes(token)) {
        // Grant access to the user
        res.status(200).send("Access granted.");
    } else {
        // Deny access
        res.status(401).send("Access denied.");
    }
});

app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

Client-Side (for context)

// Client-side logic securely sends the token to the server for authentication
fetch('http://localhost:3000/authenticate', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json'
    },
    body: JSON.stringify({ token: 'valid-user-token' })
})
.then(response => {
    if (response.ok) {
        console.log("Access granted by server.");
    } else {
        console.log("Access denied by server.");
    }
})
.catch(error => console.error('Error:', error));

Explanation of the Fix

• Server-Side Authentication: The authenticate function is now part of a server-side application using Node.js and Express. The server receives a POST request from the client containing an authentication token, which it validates against a list of valid tokens.
• Secure Communication: The client uses the fetch API to send the token to the server over a secure channel (use HTTPS in production).
• Response Handling: The server responds with appropriate HTTP status codes, allowing the client to handle access decisions based on the server's response.
• Secure Token Management: Tokens should be securely generated and managed, often using libraries or services for token management, such as JSON Web Tokens (JWTs).

This approach ensures that authentication logic and decision-making occur on the server, preventing unauthorized access from modified clients.