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Many static methods in standard java Java APIs vary their behavior according to the immediate caller's class. Such methods are considered to be caller-sensitive. For example, the java.lang.System.loadLibrary(library) method uses the immediate caller's class loader to find and dynamically load the specified library containing native method definitions. Because native code bypasses all of the security checks enforced by the Java Runtime Environment and other built-in protections provided by the Java virtual machine, only trusted code should be allowed to load native libraries. None of the loadLibrary methods in the standard APIs should be invoked on behalf of untrusted code since untrusted code may not have the necessary permissions to load the same libraries using its own class loader instance [Oracle 2014].
Noncompliant Code Example
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| Code Block | ||
|---|---|---|
| ||
// Trusted.java
import java.security.*;
public class Trusted {
public static void loadLibrary(final String library){
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
System.loadLibrary(library);
return null;
}
});
}
}
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// Untrusted.java
public class Untrusted {
private native void myMethodnativeOperation();
public static void main(String[] args) {
String library = new String("Library1NativeMethodLib");
Trusted.loadLibrary(library);
new Untrusted.nativeOperation(); // invoke the native method
}
} |
Compliant Solution
In this compliant example, the Trusted class loads any necessary native libraries during initialization and then provides access through public native method wrappers. These wrappers perform the necessary security checks and data validation to ensure that untrusted code cannot exploit the native methods (see JNI00-J. Define wrappers around native methods) .
| Code Block | ||
|---|---|---|
| ||
// Trusted.java
import java.security.*;
public class Trusted {
// load native libraries
static{
System.loadLibrary("Library1NativeMethodLib1");
System.loadLibrary("Library2NativeMethodLib2");
...
}
// private native methods
private native void nativeOperation1(byte[] data, int offset, int len);
private native void nativeOperation2(...)
...
// wrapper methodmethods performsperform SecurityManager and input validation checks
public void doOperation1(byte[] data, int offset, int len) {
// permission needed to invoke native method
securityManagerCheck();
if (data == null) {
throw new NullPointerException();
}
// copy mutable input
data = data.clone();
// validate input
if ((offset < 0) || (len < 0) || (offset > (data.length - len))) {
throw new IllegalArgumentException();
}
nativeOperationnativeOperation1(data, offset, len);
}
public void doOperation2(...){
...
}
} |
Exceptions
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Risk Assessment
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Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
JNI01-J |
| high |
| likely |
| low | P27 | L1 |
Automated Detection
Detecting calls, such as java.lang.System.loadLibrary(), that perform tasks using the immediate caller's class loader can be detected automatically. Determining whether the use of these calls is safe cannot be done automatically.
| Tool | Version | Checker | Description |
|---|---|---|---|
| Parasoft Jtest | 9.5 | CERT.JNI01.TDLIB | Protect against Library injection |
Related Guidelines
CWE-111. Direct use of unsafe JNI | |
Guideline 9-9. Safely invoke standard APIs that perform tasks using the immediate caller's class loader instance |
Bibliography
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