CWE-105: Struts: Form Field Without Validator

What is Struts: Form Field Without Validator?

• Overview: Struts: Form Field Without Validator refers to a vulnerability where a form field in a Java-based Struts application lacks corresponding validation, leading to potential security weaknesses due to insufficient input validation.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting malicious input through unvalidated form fields.
• Common attack patterns include SQL injection, cross-site scripting (XSS), and command injection through improperly validated inputs.

• Security Impact:

• Direct consequences of successful exploitation can lead to unauthorized access, data breaches, and execution of arbitrary code.
• Potential cascading effects include the compromise of connected systems or databases, and further exploitation through chained vulnerabilities.
• Business impact includes loss of customer trust, legal liabilities, and financial losses due to data breaches and system downtime.

• Prevention Guidelines:

• Specific code-level fixes include implementing strong validation rules for all form fields, using Struts validation frameworks.
• Security best practices involve regular code reviews, ensuring all input is validated and sanitized, and training developers on secure coding techniques.
• Recommended tools and frameworks include using Struts Validator (Commons Validator), incorporating OWASP's ESAPI for input validation, and employing automated security testing tools to identify unvalidated fields.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Java

Affected Technologies: Not specified

Vulnerable Code Example

// This is a vulnerable Struts form with fields that lack proper validation
import org.apache.struts.action.ActionForm;

public class UserForm extends ActionForm {
    private String username;
    private String email;

    // Getter and Setter methods for username and email
    public String getUsername() { return username; }
    public void setUsername(String username) { this.username = username; }

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

    // No validation logic here!
}

Explanation:

• The UserForm class lacks any validation logic, making it susceptible to issues like injection attacks or data corruption. Without validation, malicious users can submit harmful input, potentially compromising the application.

How to fix Struts: Form Field Without Validator?

To fix this vulnerability, it's essential to implement a validation framework that checks user input for correctness and prevents malicious data from being processed. In the context of Apache Struts, this can be accomplished by using a validation XML file or the Struts Validator Framework. This ensures that inputs are validated against a set of defined rules before the form is processed, preventing issues such as injection attacks or data corruption.

Steps to fix:

1. Use an XML validation file (such as validation.xml) to specify validation rules.
2. Ensure that each form field has appropriate validation constraints, such as checking for non-empty values, email format, length constraints, etc.
3. Use the validate method within your form class if additional server-side validation logic is needed.

Fixed Code Example

import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionErrors;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;

import javax.servlet.http.HttpServletRequest;

public class UserForm extends ActionForm {
    private String username;
    private String email;

    // Getter and Setter methods for username and email
    public String getUsername() { return username; }
    public void setUsername(String username) { this.username = username; }

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

    // Implement the validate method to enforce additional constraints
    @Override
    public ActionErrors validate(ActionMapping mapping, HttpServletRequest request) {
        ActionErrors errors = new ActionErrors();
        if (username == null || username.trim().isEmpty()) {
            errors.add("username", new ActionMessage("error.username.required"));
        }
        if (email == null || !email.matches("^[A-Za-z0-9+_.-]+@(.+)\$")) {
            errors.add("email", new ActionMessage("error.email.invalid"));
        }
        return errors;
    }
}

<!DOCTYPE validators PUBLIC "-//Apache Struts//XWork Validator 1.0.2//EN"
        "http://struts.apache.org/dtds/xwork-validator-1.0.2.dtd">
<validators>
    <field name="username">
        <field-validator type="requiredstring">
            <message key="error.username.required"/>
        </field-validator>
    </field>
    <field name="email">
        <field-validator type="email">
            <message key="error.email.invalid"/>
        </field-validator>
    </field>
</validators>

Explanation:

• UserForm.java: The validate method is overridden to add server-side validation logic, checking for empty usernames and invalid email formats. This ensures that the server processes only valid data.
• validation.xml: This file defines client-side validation rules using the Struts Validator Framework, ensuring that required fields are filled and email formats are correct. This provides an additional layer of protection by preventing invalid data from being submitted in the first place.
• These changes ensure that input is validated both on the client-side (using the XML rules) and server-side (using Java logic), offering comprehensive protection against invalid or harmful input.