CWE-205: Observable Behavioral Discrepancy

What is Observable Behavioral Discrepancy?

• Overview: Observable Behavioral Discrepancy is a vulnerability where the product's behavior reveals differences that can be observed by unauthorized actors, exposing internal states or decision processes.

• Exploitation Methods:

• Attackers can exploit this vulnerability by observing and analyzing differences in the product's responses or behaviors.
• Common attack patterns include timing attacks, where the attacker measures how long certain operations take, and differential analysis, which compares outputs or behaviors to gain insights.

• Security Impact:

• Direct consequences include unauthorized access to sensitive information or the ability to predict future states or decisions of the system.
• Potential cascading effects may include the ability to craft more sophisticated attacks based on the knowledge gained.
• Business impact could involve data breaches, loss of customer trust, or regulatory penalties due to insufficient protection of internal operations.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that all exposed behaviors are consistent and do not unintentionally reveal internal states.
• Security best practices involve implementing uniform response times and behaviors, regardless of internal conditions, to prevent timing and side-channel attacks.
• Recommended tools and frameworks include using static and dynamic analysis tools to identify and mitigate discrepancies, as well as employing frameworks that emphasize security by design.

Corgea can automatically detect and fix Observable Behavioral Discrepancy in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

function authenticateUser(username, password) {
    // Simulated user database
    const userDb = {
        "user1": "password123",
        "user2": "securepass"
    };
    
    // Vulnerable code: Different responses based on the input
    if (!userDb[username]) {
        return "Username not found";  // Observable discrepancy: reveals if a username exists
    } else if (userDb[username] !== password) {
        return "Incorrect password";  // Observable discrepancy: reveals username is correct but password is wrong
    } else {
        return "Authentication successful";
    }
}

How to fix Observable Behavioral Discrepancy?

In JavaScript, the vulnerability arises from providing differentiated messages based on the authentication input, which can be exploited to deduce valid usernames. The fix involves providing a consistent error message for any authentication failure, thus preventing potential attackers from gaining insights into the system's state.

Fixed Code Example

function authenticateUser(username, password) {
    // Simulated user database
    const userDb = {
        "user1": "password123",
        "user2": "securepass"
    };
    
    // Fixed code: Uniform error message for all authentication failures
    if (!userDb[username] || userDb[username] !== password) {
        return "Authentication failed";  // Unified error message prevents observable discrepancies
    } else {
        return "Authentication successful";
    }
}

By applying these fixes, we ensure that unauthorized users cannot derive information about the system's internal state or the existence of specific usernames, thus mitigating the risk of a CWE-205 vulnerability. The fixed code provides a single, generic error message for any authentication failure, which is a best practice to avoid revealing sensitive information.