CWE-470 Base Borrador

Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')

This vulnerability occurs when an application uses unvalidated external input, like a URL parameter or form field, to dynamically decide which class to load or which method to execute via…

Definición

What is CWE-470?

This vulnerability occurs when an application uses unvalidated external input, like a URL parameter or form field, to dynamically decide which class to load or which method to execute via reflection. An attacker can manipulate this input to force the application to load unexpected, potentially malicious code.
When an application lets user input dictate its control flow through reflection, it hands partial control of its logic to an attacker. By supplying crafted values, an attacker can bypass security checks, access unauthorized features, or trigger unexpected behaviors. The risk becomes critical if an attacker can also place malicious files on the application's classpath, allowing them to directly inject and execute their own code through this same reflection mechanism. Preventing unsafe reflection requires strict allow-listing of permitted classes or methods and rigorous validation of all dynamic input. While SAST tools can identify the vulnerable pattern, Plexicus uses AI to analyze the context and suggest precise code fixes—such as implementing a secure allow-list—transforming a complex security finding into an actionable remediation that saves development time.
Impacto en el mundo real

Real-world CVEs caused by CWE-470

  • CVE-2018-1000613

    Cryptography API uses unsafe reflection when deserializing a private key

  • CVE-2004-2331

    Database system allows attackers to bypass sandbox restrictions by using the Reflection API.

Cómo lo explotan los atacantes

Ruta del atacante paso a paso

  1. 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:

  2. 2

    A programmer might refactor this code to use reflection as follows:

  3. 3

    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.

  4. 4

    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:

  5. 5

    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.

Ejemplo de código vulnerable

Vulnerable Java

A programmer might refactor this code to use reflection as follows:

Vulnerable Java 
String ctl = request.getParameter("ctl");
  Class cmdClass = Class.forName(ctl + "Command");
  Worker ao = (Worker) cmdClass.newInstance();
  ao.doAction(request);
Ejemplo de código seguro

Secure Java

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:

Seguro 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);
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Lista de prevención

How to prevent CWE-470

  • Architecture and Design Refactor your code to avoid using reflection.
  • Architecture and Design Do not use user-controlled inputs to select and load classes or code.
  • Implementation Apply strict input validation by using allowlists or indirect selection to ensure that the user is only selecting allowable classes or code.
Señales de detección

How to detect CWE-470

Automated Static Analysis High

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Auto-corrección de Plexicus

Plexicus detecta automáticamente CWE-470 y abre un PR de corrección en menos de 60 segundos.

Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.

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Preguntas frecuentes

Frequently asked questions

¿Qué es CWE-470?

This vulnerability occurs when an application uses unvalidated external input, like a URL parameter or form field, to dynamically decide which class to load or which method to execute via reflection. An attacker can manipulate this input to force the application to load unexpected, potentially malicious code.

¿Qué gravedad tiene CWE-470?

MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.

¿Qué lenguajes o plataformas se ven afectados por CWE-470?

MITRE lists the following affected platforms: Java, PHP, Interpreted.

¿Cómo puedo prevenir CWE-470?

Refactor your code to avoid using reflection. Do not use user-controlled inputs to select and load classes or code.

¿Cómo detecta y corrige Plexicus CWE-470?

El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-470 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.

¿Dónde puedo aprender más sobre CWE-470?

MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/470.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.

Debilidades relacionadas

Weaknesses related to CWE-470

CWE-913 Padre

Improper Control of Dynamically-Managed Code Resources

This vulnerability occurs when an application fails to properly secure access to code resources that can be created or altered at runtime,…

CWE-1321 Hermano

Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Prototype pollution occurs when an application takes user-supplied input and uses it to improperly modify the properties of a JavaScript…

CWE-502 Hermano

Deserialization of Untrusted Data

This vulnerability occurs when an application accepts and processes serialized data from an untrusted source without proper validation,…

CWE-914 Hermano

Improper Control of Dynamically-Identified Variables

This vulnerability occurs when an application fails to properly secure access to variables whose names are determined at runtime, allowing…

CWE-915 Hermano

Improperly Controlled Modification of Dynamically-Determined Object Attributes

This vulnerability occurs when an application accepts user input that specifies which object attributes or fields to create or update, but…

CWE-94 Hermano

Improper Control of Generation of Code ('Code Injection')

This vulnerability occurs when an application builds executable code using unvalidated external input, such as user data. Because the…

Recursos

Further reading

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