CWE-784: Reliance on Cookies without Validation and Integrity Checking in a Security Decision

What is Reliance on Cookies without Validation and Integrity Checking in a Security Decision?

• Overview: Reliance on cookies without validation and integrity checking in a security decision is a vulnerability where software depends on cookie data for security decisions without confirming the cookie's authenticity or integrity, making it susceptible to manipulation.

• Exploitation Methods:

Attackers can modify cookies directly in the browser or through custom client-side code to inject expected values.
Common attack patterns include forging cookie values to bypass authentication or authorization checks.

• Security Impact:

Direct consequences include unauthorized access to user accounts or restricted areas.
Potential cascading effects might involve privilege escalation or data breaches.
Business impact could involve loss of customer trust, legal liabilities, and financial losses from data breaches.

• Prevention Guidelines:

Specific code-level fixes include implementing server-side validation of cookies and using secure flags.
Security best practices involve encrypting cookies and using cryptographic signing to ensure integrity.
Recommended tools and frameworks include using libraries that support secure cookie handling and implementing secure session management practices.

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Technical Details

Likelihood of Exploit: High

Affected Languages: Not Language-Specific

Affected Technologies: Web Based

Vulnerable Code Example

JavaScript Example

// Vulnerable code: Relies on cookie value without validation or integrity check
function isAuthenticated(req) {
    // Check if the user is authenticated based on a cookie value
    const userCookie = req.cookies.user;
    return userCookie === "authenticated";
}

In this vulnerable example, the isAuthenticated function relies solely on the value of a cookie to determine if a user is authenticated. This approach is insecure because an attacker could easily manipulate the cookie value to gain unauthorized access.

How to fix Reliance on Cookies without Validation and Integrity Checking in a Security Decision?

To fix this vulnerability, you should implement a system that verifies the authenticity and integrity of the cookie. This can be achieved by using signed cookies or a session management system that checks the validity of the session against a server-side store.

Use Signed Cookies: Signed cookies ensure that the data has not been tampered with. This is done by adding a cryptographic signature to the cookie.
Session Management: Use a session ID stored in a cookie to check against a server-side session store. This ensures that even if the cookie is stolen or manipulated, the session will not be valid without a matching server-side entry.
HTTPS: Always use HTTPS to protect cookies in transit. This prevents cookies from being intercepted by attackers.

Fixed Code Example

// Fixed code: Implements signed cookies to ensure integrity and validity
const cookieParser = require('cookie-parser');
const express = require('express');
const app = express();

app.use(cookieParser('your-secret-key'));  // Use a secret key for signing cookies

function isAuthenticated(req) {
    // Check if the user is authenticated by verifying the signed cookie
    const userCookie = req.signedCookies.user;

    // Check the existence and validity of the signed cookie
    return userCookie && userCookie === "authenticated";
}

app.get('/secure-endpoint', (req, res) => {
    if (isAuthenticated(req)) {
        res.send('Welcome to the secure endpoint!');
    } else {
        res.status(401).send('Unauthorized access!');
    }
});

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

In the fixed example, we use the cookie-parser middleware with a secret key to sign cookies. The req.signedCookies object is used to access cookies that are verified for integrity. This ensures that even if an attacker attempts to alter the cookie, the server will detect the tampering and the authentication will fail. Additionally, HTTPS should be used to secure cookies during transmission, although it is not explicitly shown in this code snippet. Always ensure the secret key is kept safe and not exposed in the source code.