CWE-207: Observable Behavioral Discrepancy With Equivalent Products

What is Observable Behavioral Discrepancy With Equivalent Products?

• Overview: This vulnerability occurs when a product has observable behavior differences compared to other equivalent products, allowing attackers to identify the specific product and tailor their attacks more effectively. It is crucial in environments where the product's identity or existence should remain hidden.

• Exploitation Methods:

• Attackers can perform fingerprinting to detect behavioral discrepancies and identify the specific product in use.
• Common attack patterns include passive observation of network traffic, timing analysis, error message comparison, and response pattern analysis.

• Security Impact:

• Direct consequences include enabling attackers to tailor attacks specifically for the identified product, increasing the likelihood of successful exploitation.
• Potential cascading effects include unauthorized access, data breaches, and compromised system integrity.
• Business impact may include loss of customer trust, financial loss, and potential legal ramifications if sensitive information is exposed.

• Prevention Guidelines:

• Ensure that the software behaves consistently with other equivalent products to prevent fingerprinting.
• Follow security best practices such as disabling detailed error messages, normalizing response times, and standardizing network protocol responses.
• Use recommended tools and frameworks that support obfuscation techniques and help in masking product-specific behaviors.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

function login(username, password) {
    // Simulated database check
    if (!(username in userDatabase)) {
        console.log("Login failed"); // Vulnerability: Reveals user existence indirectly
        return false;
    } else if (userDatabase[username] !== password) {
        console.log("Login failed"); // Vulnerability: Reveals that username exists indirectly
        return false;
    }
    
    console.log("Login successful");
    return true;
}

Explanation:

• Vulnerability: Although the error messages are the same, the order of checks can still reveal information. By checking the username first and then the password, an attacker could infer whether a username exists based on timing attacks or other subtle discrepancies in behavior.

How to fix Observable Behavioral Discrepancy With Equivalent Products?

To mitigate this issue, always perform both checks regardless of which fails first, and ensure the timing and behavior are consistent.

Fixed Code Example

function login(username, password) {
    // Simulated database check with consistent timing
    const userExists = username in userDatabase;
    const passwordMatches = userExists && userDatabase[username] === password;
    
    if (!userExists || !passwordMatches) {
        // Consistent error message and behavior for any login failure
        console.log("Login failed");
        return false;
    }
    
    console.log("Login successful");
    return true;
}

Explanation:

• Fix: By checking both the username and password in a manner that does not reveal which check failed, and by ensuring the timing and behavior of the function are consistent, the revised code mitigates the risk of information leakage, addressing the behavioral discrepancy vulnerability effectively.