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CWE-111: Direct Use of Unsafe JNI

Weakness ID: 111
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

When a Java application uses the Java Native Interface (JNI) to call code written in another programming language, it can expose the application to weaknesses in that code, even if those weaknesses cannot occur in Java.

Extended Description

Many safety features that programmers may take for granted simply do not apply for native code, so you must carefully review all such code for potential problems. The languages used to implement native code may be more susceptible to buffer overflows and other attacks. Native code is unprotected by the security features enforced by the runtime environment, such as strong typing and array bounds checking.

+ Time of Introduction
  • Implementation
+ Applicable Platforms



+ Common Consequences
Access Control

Technical Impact: Bypass protection mechanism

+ Demonstrative Examples

Example 1

The following code defines a class named Echo. The class declares one native method (defined below), which uses C to echo commands entered on the console back to the user. The following C code defines the native method implemented in the Echo class:

(Bad Code)
Example Language: Java 
class Echo {

public native void runEcho();
static {

public static void main(String[] args) {

new Echo().runEcho();
(Bad Code)
Example Language:
#include <jni.h>
#include "Echo.h"//the java class above compiled with javah
#include <stdio.h>

Java_Echo_runEcho(JNIEnv *env, jobject obj)
char buf[64];

Because the example is implemented in Java, it may appear that it is immune to memory issues like buffer overflow vulnerabilities. Although Java does do a good job of making memory operations safe, this protection does not extend to vulnerabilities occurring in source code written in other languages that are accessed using the Java Native Interface. Despite the memory protections offered in Java, the C code in this example is vulnerable to a buffer overflow because it makes use of gets(), which does not check the length of its input.

The Sun Java(TM) Tutorial provides the following description of JNI [See Reference]: The JNI framework lets your native method utilize Java objects in the same way that Java code uses these objects. A native method can create Java objects, including arrays and strings, and then inspect and use these objects to perform its tasks. A native method can also inspect and use objects created by Java application code. A native method can even update Java objects that it created or that were passed to it, and these updated objects are available to the Java application. Thus, both the native language side and the Java side of an application can create, update, and access Java objects and then share these objects between them.

The vulnerability in the example above could easily be detected through a source code audit of the native method implementation. This may not be practical or possible depending on the availability of the C source code and the way the project is built, but in many cases it may suffice. However, the ability to share objects between Java and native methods expands the potential risk to much more insidious cases where improper data handling in Java may lead to unexpected vulnerabilities in native code or unsafe operations in native code corrupt data structures in Java. Vulnerabilities in native code accessed through a Java application are typically exploited in the same manner as they are in applications written in the native language. The only challenge to such an attack is for the attacker to identify that the Java application uses native code to perform certain operations. This can be accomplished in a variety of ways, including identifying specific behaviors that are often implemented with native code or by exploiting a system information exposure in the Java application that reveals its use of JNI [See Reference].

+ Potential Mitigations

Phase: Implementation

Implement error handling around the JNI call.

Phases: Architecture and Design; Implementation

Strategy: Refactoring

Do not use JNI calls if you don't trust the native library.

Phases: Architecture and Design; Implementation

Strategy: Refactoring

Be reluctant to use JNI calls. A Java API equivalent may exist.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Development Concepts (primary)699
Seven Pernicious Kingdoms (primary)700
ChildOfWeakness BaseWeakness Base695Use of Low-Level Functionality
Research Concepts (primary)1000
ChildOfCategoryCategory859CERT Java Secure Coding Section 14 - Platform Security (SEC)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfCategoryCategory1001SFP Secondary Cluster: Use of an Improper API
Software Fault Pattern (SFP) Clusters (primary)888
+ Causal Nature


+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
7 Pernicious KingdomsUnsafe JNI
CERT Java Secure CodingSEC08-JDefine wrappers around native methods
Software Fault PatternsSFP3Use of an improper API
+ References
Fortify Software. "Fortify Descriptions". <>.
B. Stearns. "The Java(TM) Tutorial: The Java Native Interface". Sun Microsystems. 2005. <>.
+ Content History
Submission DateSubmitterOrganizationSource
7 Pernicious KingdomsExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Demonstrative_Example, Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Other_Notes, References, Taxonomy_Mappings, Weakness_Ordinalities
2008-11-24CWE Content TeamMITREInternal
updated Description, Other_Notes
2009-10-29CWE Content TeamMITREInternal
updated Description, Other_Notes
2011-03-29CWE Content TeamMITREInternal
updated Demonstrative_Examples
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2013-02-21CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Unsafe JNI

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Page Last Updated: January 18, 2017