CWE-179: Incorrect Behavior Order: Early Validation

What is Incorrect Behavior Order: Early Validation?

• Overview: Incorrect Behavior Order: Early Validation (CWE-179) occurs when a software application validates input before it has been fully processed or transformed. This can allow attackers to bypass the validation process by introducing dangerous inputs that only become harmful after the input has been modified or canonicalized.

• Exploitation Methods:

• Attackers can exploit this vulnerability by providing input that appears safe during initial validation but transforms into harmful input after processing.
• Common attack patterns include input that changes character encodings, uses escape sequences, or relies on data transformations to bypass validation checks.

• Security Impact:

• Direct consequences include the potential execution of malicious code, data corruption, or unauthorized access to system resources.
• Potential cascading effects could involve the compromise of other systems or data due to the initial breach.
• Business impact may include data breaches, loss of customer trust, legal consequences, and financial losses.

• Prevention Guidelines:

• Specific code-level fixes involve ensuring input validation occurs after all data transformations or canonicalizations are complete.
• Security best practices include adopting a "validate after processing" approach and integrating security checks throughout the data handling lifecycle.
• Recommended tools and frameworks include using libraries that automatically handle input validation and canonicalization securely, and employing static analysis tools to detect improper validation sequences in code.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

function sanitizeInput(userInput) {
    // Vulnerable: Incorrect behavior order
    // Input is validated before it is sanitized, allowing potential bypass
    if (userInput.length > 5) {
        return "Input too long";
    }

    // Sanitization happens after validation, which is incorrect
    const sanitizedInput = userInput.replace(/</g, "&lt;").replace(/>/g, "&gt;");
    return sanitizedInput;
}

console.log(sanitizeInput("<script>"));  // Expected to sanitize, but early validation prevents it

How to fix Incorrect Behavior Order: Early Validation?

To address this vulnerability, ensure that input is sanitized before any validation checks are applied. By doing so, you guarantee that the validation logic operates on a version of the input that is free from potentially malicious content. This order of operations is critical for maintaining the security and integrity of application logic that depends on sanitized input.

Fixed Code Example

function sanitizeInput(userInput) {
    // Correct order: sanitize before validation
    // First, sanitize the input to remove any harmful content
    const sanitizedInput = userInput.replace(/</g, "&lt;").replace(/>/g, "&gt;");

    // Then validate the sanitized input
    if (sanitizedInput.length > 5) {
        return "Input too long";
    }

    return sanitizedInput;
}

console.log(sanitizeInput("<script>"));  // Properly sanitizes before validating

In both examples, the key fix was to swap the order of sanitization and validation, ensuring that the input is sanitized first and then validated. This prevents attackers from exploiting the validation logic with unsanitized input. The corrected example demonstrates best practices by ensuring that potentially harmful content is neutralized before any validation checks are performed.