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The default {{SecurityManager}} checks whether the caller of a particular method has sufficient permissions to proceed with an action. An action is a level of access, for instance, the actions for {{java.io.FilePermission}} are "read""read", "write""write", "execute""execute", and "delete""delete" \[[Sun 06|AA. Java References#Sun 06]\]. The Permission Descriptions and Risks guide \[[Permissions 08|AA. Java References#Permissions 08]\] enumerates the default permissions and the risks associated with granting these permissions to Java code. |
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class LoadLibrary {
private void loadLibrary() {
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
// privileged code
System.loadLibrary("awt""awt");
// perform some sensitive operation like setting the default exception handler
MyExceptionReporter.setExceptionReporter(reporter);
return null;
}
});
}
}
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class LoadLibrary {
private void loadLibrary() {
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
// privileged code
System.loadLibrary("awt""awt");
SecurityManager sm = System.getSecurityManager();
if(sm != null) {
sm.checkPermission(new ExceptionReporterPermission(""exc.reporter""));
}
// perform some sensitive operation like setting the default exception handler
MyExceptionReporter.setExceptionReporter(reporter);
return null;
}
});
}
}
class ExceptionReporterPermission extends BasicPermission {
public ExceptionReporterPermission(String permName) {
super(permName);
}
// Even though the actions parameter is ignored, this constructor has to be defined
public ExceptionReporterPermission(String permName, String actions) {
super(permName, actions);
}
}
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Assuming that the above sources reside in the c:\package directory on a Windows based system, for example, the policy file needs to grant two permissions, ExceptionReporterPermission exc.reporter and RuntimePermission loadlibrary.awt.
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grant codeBase ""file:c:\\package"" { // For *nix, file:${user.home}/package/ permission ExceptionReporterPermission ""exc.reporter""; permission java.lang.RuntimePermission ""loadLibrary.awt""; }; |
Risk Assessment
Running Java code without defining custom permissions where default ones are inapplicable can leave an application open to privilege escalation vulnerabilities.
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Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
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\[[API 06|AA. Java References#API 06]\] [Class SecurityManager|http://java.sun.com/javase/6/docs/api/java/lang/SecurityManager.html] \[[Oaks 01|AA. Java References#Oaks 01]\] Chapter 5: The Access Controller, "Permissions""Permissions" \[[Policy 02|AA. Java References#Policy 02]\] \[[Sun 06|AA. Java References#Sun 06]\] [Permission Descriptions and Risks|http://java.sun.com/javase/6/docs/technotes/guides/security/permissions.html] |
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SEC07-J. Do not grant untrusted code access to classes existing in forbidden packages 02. Platform Security (SEC) SEC09-J. Prefer using SSLSockets over Sockets for secure data exchange