Struts: Form Field Without Validator

Description

Omitting validation for even a single input field may give attackers the leeway they need to compromise the product. Although J2EE applications are not generally susceptible to memory corruption attacks, if a J2EE application interfaces with native code that does not perform array bounds checking, an attacker may be able to use an input validation mistake in the J2EE application to launch a buffer overflow attack.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the following example the Java class RegistrationForm is a Struts framework ActionForm Bean that will maintain user input data from a registration webpage for an online business site. The user will enter registration data and, through the Struts framework, the RegistrationForm bean will maintain the user data in the form fields using the private member variables. The RegistrationForm class uses the Struts validation capability by extending the ValidatorForm class and including the validation for the form fields within the validator XML file, validator.xml.

public class RegistrationForm extends org.apache.struts.validator.ValidatorForm {

  // private variables for registration form
  private String name;
  private String address;
  private String city;
  private String state;
  private String zipcode;
  private String phone;
  private String email;

  public RegistrationForm() {
    super();
  }

  // getter and setter methods for private variables
  ...

}

The validator XML file, validator.xml, provides the validation for the form fields of the RegistrationForm.

<form-validation>
  <formset>
    <form name="RegistrationForm">
      <field property="name" depends="required">
        <arg position="0" key="prompt.name"/>
      </field>
      <field property="address" depends="required">
        <arg position="0" key="prompt.address"/>
      </field>
      <field property="city" depends="required">
        <arg position="0" key="prompt.city"/>
      </field>
      <field property="state" depends="required,mask">
        <arg position="0" key="prompt.state"/>
        <var>
          <var-name>mask</var-name>
          <var-value>[a-zA-Z]{2}</var-value>
        </var>
      </field>
      <field property="zipcode" depends="required,mask">
        <arg position="0" key="prompt.zipcode"/>
        <var>
          <var-name>mask</var-name>
          <var-value>\d{5}</var-value>
        </var>
      </field>
    </form>
  </formset>
</form-validation>

However, in the previous example the validator XML file, validator.xml, does not provide validators for all of the form fields in the RegistrationForm. Validator forms are only provided for the first five of the seven form fields. The validator XML file should contain validator forms for all of the form fields for a Struts ActionForm bean. The following validator.xml file for the RegistrationForm class contains validator forms for all of the form fields.

<form-validation>
  <formset>
    <form name="RegistrationForm">
      <field property="name" depends="required">
        <arg position="0" key="prompt.name"/>
      </field>
      <field property="address" depends="required">
        <arg position="0" key="prompt.address"/>
      </field>
      <field property="city" depends="required">
        <arg position="0" key="prompt.city"/>
      </field>
      <field property="state" depends="required,mask">
        <arg position="0" key="prompt.state"/>
        <var>
          <var-name>mask</var-name>
          <var-value>[a-zA-Z]{2}</var-value>
        </var>
      </field>
      <field property="zipcode" depends="required,mask">
        <arg position="0" key="prompt.zipcode"/>
        <var>
          <var-name>mask</var-name>
          <var-value>\d{5}</var-value>
        </var>
      </field>
      <field property="phone" depends="required,mask">
        <arg position="0" key="prompt.phone"/>
        <var>
          <var-name>mask</var-name>
          <var-value>^([0-9]{3})(-)([0-9]{4}|[0-9]{4})$</var-value>
        </var>
      </field>
      <field property="email" depends="required,email">
        <arg position="0" key="prompt.email"/>
      </field>
    </form>
  </formset>
</form-validation>

See Also