CWE-104: Struts: Form Bean Does Not Extend Validation Class

What is Struts: Form Bean Does Not Extend Validation Class?

• Overview: This vulnerability occurs when a form bean in a Struts application does not extend the ActionForm subclass from the Validator framework, leading to insufficient input validation, which can result in various security issues.

• Exploitation Methods:

• Attackers can exploit this vulnerability by submitting malicious input that bypasses validation checks.
• Common attack patterns include SQL injection, cross-site scripting (XSS), and other injection attacks due to unvalidated input.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access, data corruption, and data leakage.
• Potential cascading effects include compromised application integrity and further system-level security breaches.
• Business impact can range from financial loss, reputational damage, to regulatory non-compliance penalties.

• Prevention Guidelines:

• Ensure all form beans extend the appropriate ActionForm subclass within the Validator framework.
• Implement comprehensive input validation for all user inputs, including client-side and server-side checks.
• Use recommended tools and frameworks such as Struts Validator framework to enforce validation rules consistently.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Java

Affected Technologies: Not specified

In order to use the Struts Validator, a form must extend one of the following: ValidatorForm, ValidatorActionForm, DynaValidatorActionForm, and DynaValidatorForm. One of these classes must be extended because the Struts Validator ties in to the application by implementing the validate() method in these classes. Forms derived from the ActionForm and DynaActionForm classes cannot use the Struts Validator.

Vulnerable Code Example

// This form bean does not extend the ActionForm or ValidatorForm class, 
// which means it lacks built-in validation mechanisms.
// This makes the application susceptible to insufficient input validation,
// as there is no automatic checking of user inputs for correctness or safety.

public class UserForm { 
    private String username;
    private String password;

    // Getters and setters omitted for brevity
}

How to fix Struts: Form Bean Does Not Extend Validation Class?

To fix this vulnerability, we should ensure that our form beans extend from ValidatorForm or ActionForm, which are part of the Struts framework. These classes provide a means to perform input validation before the data is processed by the application. By leveraging these classes, we can define validation rules either in the form of XML configuration or directly in the Java code, ensuring that inputs are checked for correctness, format, and length, thereby preventing invalid data from entering the business logic layer.

Specifically, in Struts, extending ValidatorForm allows us to use the Struts Validator framework, where validation rules can be specified in a validation.xml file. This approach centralizes the validation logic and makes it easier to maintain and update.

Fixed Code Example

// The form bean now extends the ValidatorForm class, 
// enabling it to use Struts' validation framework.
// This ensures that all inputs are properly validated according to rules defined in validation.xml,
// thus mitigating the risk of processing invalid or malicious data.

import org.apache.struts.validator.ValidatorForm;

public class UserForm extends ValidatorForm { 
    private String username;
    private String password;

    // Getters and setters omitted for brevity
}

Example validation.xml:

<form-validation>
    <formset>
        <form name="UserForm">
            <field property="username" depends="required">
                <arg0 key="error.username.required"/>
            </field>
            <field property="password" depends="required,minlength">
                <arg0 key="error.password.required"/>
                <arg1 key="error.password.minlength"/>
                <var>
                    <var-name>minlength</var-name>
                    <var-value>8</var-value>
                </var>
            </field>
        </form>
    </formset>
</form-validation>

By extending ValidatorForm, the UserForm class can leverage the Struts validation framework to enforce input validation rules before processing data. This practice helps in mitigating risks related to improper data handling, ensuring that only sanitized and validated data reaches the application's core logic. This approach not only enhances security but also improves the maintainability and readability of the validation logic.