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Sometimes, stronger restrictions than those provided by the default security manager are necessary. Custom permissions prove to be more suitable for privilege separation in such cases. Failure to provide custom permissions when no corresponding default permissions exist can lead to privilege escalation vulnerabilities where untrusted callers can execute restricted operations or actions.

Noncompliant Code Example

This noncompliant code example contains a privileged block that is used to perform two sensitive operations, loading a library and setting the default exception handler. When used, the default security manager does not permit the loading of the library unless the RuntimePermission loadLibrary.awt is granted in the policy file. However, the security manager does not automatically guard a caller from performing the second sensitive operation of setting the default exception handler. This is because the permission for this operation is not non-default and, consequently, unavailable. This security weakness can be exploited, for example, by programming and installing an exception handler that reveals information that a legitimate handler would filter out.

class LoadLibrary {
  private void loadLibrary() {
    AccessController.doPrivileged(new PrivilegedAction() {
      public Object run() {
        // privileged code
        System.loadLibrary("awt");
        // perform some sensitive operation like setting the default exception handler
        MyExceptionReporter.setExceptionReporter(reporter); 
        return null; 
      }
    });		  
  }
}

Compliant Solution

This compliant solution defines a custom permission ExceptionReporterPermission with target exc.reporter to prohibit illegitimate callers from setting the default exception handler. This can be achieved by subclassing BasicPermission which allows binary style permissions (either allow or disallow).

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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 permissions are inapplicable can leave an application open to privilege escalation vulnerabilities.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this guideline on the CERT website.

Related Guidelines

MITRE CWE: CWE-732, "Incorrect Permission Assignment for Critical Resource"

Bibliography

\[[API 2006|AA. Bibliography#API 06]\] [Class SecurityManager|http://java.sun.com/javase/6/docs/api/java/lang/SecurityManager.html]
\[[Oaks 2001|AA. Bibliography#Oaks 01]\] Chapter 5: The Access Controller, "Permissions"
\[[Policy 2002|AA. Bibliography#Policy 02]\]
\[[Sun 2006|AA. Bibliography#Sun 06]\] [Permission Descriptions and Risks|http://java.sun.com/javase/6/docs/technotes/guides/security/permissions.html]

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