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Native methods are defined in Java and written in traditional languages such as C and C++ \[[JNI 2006|AA. Bibliography#JNI 06]\]. The added extensibility comes at the cost of flexibility and portability as the code no longer conforms to the policies enforced by Java. In the past, native methods were used for performing platform specific operations, interfacing with legacy library code and improving program performance \[[Bloch 2008|AA. Bibliography#Bloch 08]\]. Although this is notno longer completely true in present times (---because of poor portability, safety and (quite ironically,) performance issues), ---native code is still used to interface with legacy code.

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Noncompliant Code Example

Security Native method invocations bypass security manager checks are not automatically enforced in case of native method invocations. Additionally, as demonstrated in this noncompliant code example, it is easy to overlook proper input validation before the callnative method invocation. The doOperation() method invokes the nativeOperation() native method but fails to provide adequate input validation. AlsoFurther, untrusted callers can invoke the native method because its access specifier of the native method is public which allows untrusted callers to invoke the method.

public final class NativeMethod {

  // public native method
  public native void nativeOperation(byte[] data, int offset, int len);

  // wrapper method that does not perform anylacks security checks orand input validation
  public void doOperation(byte[] data, int offset, int len) {
    nativeOperation(data, offset, len);
  }
  
  static {
    // load native library in static initializer of class
    System.loadLibrary("NativeMethodLib"); 
  }
}

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This compliant solution declares the native method private and defines a public wrapper that calls the securityManagerCheck() method. This The wrapper method performs routine permission checking to determine if whether the succeeding operations can are permitted to continue. This is followed by the creation of a defensive copy of the mutable input array , data and input data as well as by range checking of the parameters. Finally the The nativeOperation() method is thus called with safe inputs. Ensure Note that the validation checks must produce outputs that are coherent with conform to the input requirements of the native implementations/libraries.

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Failure to define wrappers around native methods can allow unprivileged callers to invoke them and thus exploit inherent vulnerabilities such as the ones those resulting from invalid input validationinputs.

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