CWE-578: EJB Bad Practices: Use of Class Loader

Description

The product violates the Enterprise JavaBeans (EJB) specification by using the class loader.

The Enterprise JavaBeans specification requires that every bean provider follow a set of programming guidelines designed to ensure that the bean will be portable and behave consistently in any EJB container. In this case, the product violates the following EJB guideline: "The enterprise bean must not attempt to create a class loader; obtain the current class loader; set the context class loader; set security manager; create a new security manager; stop the JVM; or change the input, output, and error streams." The specification justifies this requirement in the following way: "These functions are reserved for the EJB container. Allowing the enterprise bean to use these functions could compromise security and decrease the container's ability to properly manage the runtime environment."

Potential Impact

Confidentiality, Integrity, Availability, Other

Execute Unauthorized Code or Commands, Varies by Context

Demonstrative Examples

The following Java example is a simple stateless Enterprise JavaBean that retrieves the interest rate for the number of points for a mortgage. The interest rates for various points are retrieved from an XML document on the local file system, and the EJB uses the Class Loader for the EJB class to obtain the XML document from the local file system as an input stream.

Bad

@Statelesspublic class InterestRateBean implements InterestRateRemote {
                     
                        private Document interestRateXMLDocument = null;
                           public InterestRateBean() {
                              try {
                                    
                                       
                                       // get XML document from the local filesystem as an input stream
                                       
                                       
                                       // using the ClassLoader for this class
                                       ClassLoader loader = this.getClass().getClassLoader();InputStream in = loader.getResourceAsStream(Constants.INTEREST_RATE_FILE);
                                 
                              
                           
                           
                           DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();DocumentBuilder db = dbf.newDocumentBuilder();interestRateXMLDocument = db.parse(interestRateFile);} catch (IOException ex) {...}
                     }
                     
                        public BigDecimal getInterestRate(Integer points) {return getInterestRateFromXML(points);}
                           
                           /* member function to retrieve interest rate from XML document on the local file system */
                           
                           private BigDecimal getInterestRateFromXML(Integer points) {...}
                     }

This use of the Java Class Loader class within any kind of Enterprise JavaBean violates the restriction of the EJB specification against obtaining the current class loader as this could compromise the security of the application using the EJB.

An EJB is also restricted from creating a custom class loader and creating a class and instance of a class from the class loader, as shown in the following example.

Bad

@Statelesspublic class LoaderSessionBean implements LoaderSessionRemote {
                     
                        public LoaderSessionBean() {try {ClassLoader loader = new CustomClassLoader();Class c = loader.loadClass("someClass");Object obj = c.newInstance();/* perform some task that uses the new class instance member variables or functions */...} catch (Exception ex) {...}}
                           public class CustomClassLoader extends ClassLoader {
                           }
                     }

Mitigations & Prevention

Architecture and DesignImplementation

Do not use the Class Loader when writing EJBs.

Taxonomy Mappings

Software Fault Patterns: SFP3 — Use of an improper API

Frequently Asked Questions

What is CWE-578?

CWE-578 (EJB Bad Practices: Use of Class Loader) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Variant-level weakness. The product violates the Enterprise JavaBeans (EJB) specification by using the class loader.

How can CWE-578 be exploited?

Attackers can exploit CWE-578 (EJB Bad Practices: Use of Class Loader) to execute unauthorized code or commands, varies by context. This weakness is typically introduced during the Implementation phase of software development.

How do I prevent CWE-578?

Key mitigations include: Do not use the Class Loader when writing EJBs.

What is the severity of CWE-578?

CWE-578 is classified as a Variant-level weakness (Low-Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.