Home > CWE List > CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection') (4.17) |
|
CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
View customized information:
For users who are interested in more notional aspects of a weakness. Example: educators, technical writers, and project/program managers.
For users who are concerned with the practical application and details about the nature of a weakness and how to prevent it from happening. Example: tool developers, security researchers, pen-testers, incident response analysts.
For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). Example: tool developers, security researchers.
For users who wish to see all available information for the CWE/CAPEC entry.
For users who want to customize what details are displayed.
×
Edit Custom FilterThe product uses external input with reflection to select which classes or code to use, but it does not sufficiently prevent the input from selecting improper classes or code.
If the product uses external inputs to determine which class to instantiate or which method to invoke, then an attacker could supply values to select unexpected classes or methods. If this occurs, then the attacker could create control flow paths that were not intended by the developer. These paths could bypass authentication or access control checks, or otherwise cause the product to behave in an unexpected manner. This situation becomes a doomsday scenario if the attacker can upload files into a location that appears on the product's classpath (CWE-427) or add new entries to the product's classpath (CWE-426). Under either of these conditions, the attacker can use reflection to introduce new, malicious behavior into the product.
![]()
![]() ![]()
![]()
![]()
![]()
![]()
![]()
Example 1 A common reason that programmers use the reflection API is to implement their own command dispatcher. The following example shows a command dispatcher that does not use reflection: (good code)
Example Language: Java
String ctl = request.getParameter("ctl");
Worker ao = null; if (ctl.equals("Add")) { ao = new AddCommand(); }else if (ctl.equals("Modify")) { ao = new ModifyCommand(); }else { throw new UnknownActionError(); }ao.doAction(request); A programmer might refactor this code to use reflection as follows: (bad code)
Example Language: Java
String ctl = request.getParameter("ctl");
Class cmdClass = Class.forName(ctl + "Command"); Worker ao = (Worker) cmdClass.newInstance(); ao.doAction(request); The refactoring initially appears to offer a number of advantages. There are fewer lines of code, the if/else blocks have been entirely eliminated, and it is now possible to add new command types without modifying the command dispatcher. However, the refactoring allows an attacker to instantiate any object that implements the Worker interface. If the command dispatcher is still responsible for access control, then whenever programmers create a new class that implements the Worker interface, they must remember to modify the dispatcher's access control code. If they do not modify the access control code, then some Worker classes will not have any access control. One way to address this access control problem is to make the Worker object responsible for performing the access control check. An example of the re-refactored code follows: (bad code)
Example Language: Java
String ctl = request.getParameter("ctl");
Class cmdClass = Class.forName(ctl + "Command"); Worker ao = (Worker) cmdClass.newInstance(); ao.checkAccessControl(request); ao.doAction(request); Although this is an improvement, it encourages a decentralized approach to access control, which makes it easier for programmers to make access control mistakes. This code also highlights another security problem with using reflection to build a command dispatcher. An attacker can invoke the default constructor for any kind of object. In fact, the attacker is not even constrained to objects that implement the Worker interface; the default constructor for any object in the system can be invoked. If the object does not implement the Worker interface, a ClassCastException will be thrown before the assignment to ao, but if the constructor performs operations that work in the attacker's favor, the damage will already have been done. Although this scenario is relatively benign in simple products, in larger products where complexity grows exponentially it is not unreasonable that an attacker could find a constructor to leverage as part of an attack. Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.
![]()
More information is available — Please edit the custom filter or select a different filter. |
Use of the Common Weakness Enumeration (CWE™) and the associated references from this website are subject to the Terms of Use. CWE is sponsored by the U.S. Department of Homeland Security (DHS) Cybersecurity and Infrastructure Security Agency (CISA) and managed by the Homeland Security Systems Engineering and Development Institute (HSSEDI) which is operated by The MITRE Corporation (MITRE). Copyright © 2006–2025, The MITRE Corporation. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. |