CWE-110: Struts: Validator Without Form Field

What is Struts: Validator Without Form Field?

• Overview: This vulnerability occurs when the validation logic in a Struts application is outdated or incomplete, resulting in validation fields that don't match the form fields they are supposed to validate. This inconsistency suggests that the validation logic has not been properly maintained, potentially allowing unexpected inputs.

• Exploitation Methods:

• Attackers can exploit this by submitting unexpected input that bypasses the validation logic, as the validation fields are not present or incorrectly mapped.
• Common attack patterns involve bypassing input validation to insert malicious data or unexpected input that the application does not handle properly.

• Security Impact:

• Direct consequences include the execution of unvalidated or malicious input, leading to unexpected application behavior.
• Potential cascading effects include security vulnerabilities such as buffer overflows if the application interacts with native code lacking proper bounds checking.
• Business impact can range from data breaches to service disruptions and loss of customer trust.

• Prevention Guidelines:

• Specific code-level fixes include regularly updating and synchronizing the validation logic with the form fields in ActionForm classes.
• Security best practices involve thorough testing and code reviews to ensure validation logic is current and comprehensive.
• Recommended tools and frameworks include using automated tools for static code analysis and adopting frameworks that enforce stricter validation logic maintenance.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Java

Affected Technologies: Not specified

Vulnerable Code Example

Java Example

// UserRegistrationAction.java
public class UserRegistrationAction extends Action {
    // Validator configuration expects an "email" field to be validated
    // However, the form does not include an "email" input field
    private String username;
    private String password;
    // Missing email field leads to validation mismatch
}

<!-- validation.xml -->
<field name="email">
    <!-- Validator configuration for email field -->
    <field-validator type="email">
        <message>Email is not valid</message>
    </field-validator>
</field>

Vulnerability Explanation

• Problem: The Struts validation configuration (validation.xml) specifies a validator for the email field, but the corresponding Java form (UserRegistrationAction.java) does not include an email field.
• Impact: This mismatch indicates that the validation logic is out of sync with the form, which can lead to security issues such as improper input processing and validation bypass. It may also cause runtime errors if the system attempts to validate a non-existent field.

How to fix Struts: Validator Without Form Field?

1. Ensure Consistency: Make sure that every field configured for validation in validation.xml is present in the form class.
2. Regular Audits: Periodically review and update validation rules and forms to ensure they are in sync, especially after changes in business requirements or application logic.
3. Testing: Implement automated tests that check for mismatches between form fields and validation configurations.

Fixed Code Example

Java Example

// UserRegistrationAction.java
public class UserRegistrationAction extends Action {
    // Added "email" field to match the validator configuration
    private String username;
    private String password;
    private String email; // Now the form is consistent with the validation rules

    // Getters and setters for email
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

<!-- validation.xml -->
<field name="email">
    <!-- Validator configuration for email field -->
    <field-validator type="email">
        <message>Email is not valid</message>
    </field-validator>
</field>

Fixed Code Explanation

• Fixed Line: Added the email field to the UserRegistrationAction class to align with the validation.xml configuration.
• Best Practices: Regular checks for consistency between form fields and validator configurations prevent mismatches and potential security vulnerabilities. Ensuring that all expected inputs are properly validated according to the application's security requirements is crucial. Additionally, providing getters and setters for the fields ensures that they can be accessed and modified appropriately within the application.