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Certain combinations of permissions can produce significant capability increases and should not be granted. Other permissions should be granted only to special code.

AllPermission

The permission java.security.AllPermission implies all permissions and grants all possible permissions to code. This facility was included for routine testing purposes to make it less cumbersome to deal with to reduce the burden of managing a multitude of permissions and for use when the during routine testing as well as when a body of code is completely trusted. Code is typically granted AllPermission using via the security policy file but ; it is also possible to programmatically associate AllPermission with a ProtectionDomain, programatically. This permission is dangerous in production environments and must never be granted to untrusted code.

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. Never grant AllPermission to untrusted code.

ReflectPermission, suppressAccessChecks

Granting ReflectPermission on the target suppressAccessChecks suppresses all standard Java language access checks when the permitted class attempts to operate on package-private, protected, or private members of another class. Consequently, the permitted class can obtain permissions to examine any field or invoke any method belonging to an arbitrary class [Reflect 2006]. As a result, ReflectPermission must never be granted with target suppressAccessChecks.

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 the security policy file used by the security manager. Alternatively, Program code can obtain a permission object can be obtained in the code by subclassing the java.security.Permission class ( or any subclass such as BasicPermission). AllPermission can be granted to a ProtectionDomain using such an object. This is again a bad practice.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 codecheck
FilePermission perm =
    new java.io.FilePermission("/tmp/JavaFile", "read");
AccessController.checkPermission(perm);
// ...

Always assign appropriate permissions to code. When more control over Define custom permissions when the granularity of the standard permissions is required, define custom permissions. (SEC10-J. Define custom security permissions for fine grained security) insufficient.

Noncompliant Code Example (PermissionCollection)

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

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

...

Compliant Solution

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

protected PermissionCollection getPermissions(CodeSource cs) {
  PermissionCollection pc = super.getPermissions(cs);
  // add fine-grainedOther permissions
  return pc;
}

Exceptions

EX1ENV03-J-EX0: It may be necessary to grant AllPermission to trusted library code so that callbacks work as expected. For example, it is a 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 "file:${{java.ext.dirs}}/*" {
  permission java.security.AllPermission;
};

Risk Assessment

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

Automated Detection

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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

References

\[[API 2006|AA. Java References#API 06]\] [Class AllPermission|http://java.sun.com/javase/6/docs/api/java/security/AllPermission.html]
\[[Gong 2003|AA. Java References#Gong 03]\]
\[[Security 2006|AA. Java References#Security 06]\] [Security Architecture|http://java.sun.com/javase/6/docs/technotes/guides/security/spec/security-spec.doc.html]

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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Image Added Image Added Image AddedENV02-J. Create a secure sandbox using a Security Manager      01. Runtime Environment (ENV)      ENV04-J. Do not grant ReflectPermission with target suppressAccessChecks