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According to the technical note Permissions in the Java SE 6 Development Kit [Permissions 2008], Section ReflectPermission, target suppressAccessChecks:

Warning: Extreme caution should be taken before granting this permission to code, for it provides the ability to access fields and invoke methods in a class. This includes not only public, but protected and private fields and methods as well.

RuntimePermission, createClassLoader

The permission java.lang.RuntimePermission applied to target createClassLoader grants code the permission to create a ClassLoader object. This permission is extremely dangerous because malicious code can create its own custom class loader and load classes by assigning them arbitrary permissions. A custom class loader can define a class (or ProtectionDomain) with permissions that override any restrictions specified in the systemwide security policy file.

Permissions in the Java SE 6 Development Kit [Permissions 2008] states:

This is an extremely dangerous permission to grant. Malicious applications that can instantiate their own class loaders could then load their own rogue classes into the system. These newly loaded classes could be placed into any protection domain by the class loader, thereby automatically granting the classes the permissions for that domain.

Noncompliant Code Example (Security Policy File)

This noncompliant example grants AllPermission to the klib library:

// Grant the klib library AllPermission  
grant codebase "file:${klib.home}/j2se/home/klib.jar" { 
  permission java.security.AllPermission; 
}; 

The permission itself is specified in the security policy file used by the security manager. Program code can obtain a permission object by subclassing the java.security.Permission class or any of its subclasses (BasicPermission, for example). The code can use the resulting object to grant AllPermission to a ProtectionDomain.

Compliant Solution

This compliant solution shows a policy file that can be used to enforce fine-grained permissions:

grant codeBase 
    "file:${klib.home}/j2se/home/klib.jar", signedBy "Admin" {
  permission java.io.FilePermission "/tmp/*", "read";
  permission java.io.SocketPermission "*", "connect";
};

To check whether the caller has the requisite permissions, standard Java APIs use code such as the following:

// Security manager check
FilePermission perm =
    new java.io.FilePermission("/tmp/JavaFile", "read");
AccessController.checkPermission(perm);
// ...

Always assign appropriate permissions to code. Define custom permissions when the granularity of the standard permissions is insufficient.

Noncompliant Code Example (PermissionCollection)

This noncompliant code example shows an overridden getPermissions() method, defined in a custom class loader. It grants java.lang.ReflectPermission with target suppressAccessChecks to any class that it loads.

protected PermissionCollection getPermissions(CodeSource cs) {
  PermissionCollection pc = super.getPermissions(cs);
  pc.add(new ReflectPermission("suppressAccessChecks"));   // Permission to create a class loader
  // Other permissions
  return pc;
}

Compliant Solution

This compliant solution does not grant java.lang.ReflectPermission with target suppressAccessChecks to any class that it loads:

protected PermissionCollection getPermissions(CodeSource cs) {
  PermissionCollection pc = super.getPermissions(cs);
  // Other permissions
  return pc;
}

Exceptions

ENV03-J-EX0: It may be necessary to grant AllPermission to trusted library code so that callbacks work as expected. For example, it is common practice, and acceptable, to grant AllPermission to the optional Java packages (extension libraries):

// Standard extensions extend the core platform and are granted all permissions by default
grant codeBase "TODO" {
  permission java.security.AllPermission;
};

Risk Assessment

Granting AllPermission to untrusted code allows it to perform privileged operations.

Automated Detection

Static detection of potential uses of dangerous permissions is a trivial search. Automated determination of the correctness of such uses is not feasible.

Related Vulnerabilities

CVE-2007-5342 describes a vulnerability in Apache Tomcat 5.5.9 through 5.5.25 and 6.0.0 through 6.0.15. The security policy used in the JULI logging component failed to restrict certain permissions for web applications. An attacker could modify the log level, directory, or prefix attributes in the org.apache.juli.FileHandler handler, permitting them to modify logging configuration options and overwrite arbitrary files.

Related Guidelines

Android Implementation Details

The java.security package exists on Android for compatibility purposes only, and it should not be used. Android uses another permission mechanism for security purposes.

Bibliography

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