Java Applet Security

Diana DongCS 265

Spring 2004

The Problem

Millions of users download Java applets everyday, sometimes without prior approval from the user

How to ensure malicious applets will not wreak havoc on the local machine?

Sandbox Idea

A place where Java applet code can be executed, but no areas outside of the sandbox can be accessed by the applet.

Removes the responsibility of checking applet source from the user

Ensures execution of malicious applet will not do damage to the local machine

Sandbox cont'd

Sandbox prohibits: File system access Network access Creation of process Process acess

4 Major Components of the Sandbox

Java Virtual Machine (JVM) built-in features

Class loader Class file verifier Security manager

JVM Built-in Features

Type-safe reference casting Structured memory access (no

pointers) Automatic garbage collection

(can't explicitly free allocated memory)

Array bounds checking

Class Loader

Responsible for importing binary data that defines the running program's classes and interfaces

Two types of class loaders: primordial class loader and class loader objects

Class Loader cont'd

Primordial class loader loads trusted classes, such as the Java API. Classes that are loaded this way becomes part of the JVM.

Class loader objects are untrusted objects loaded into the JVM and instantiated like any other object

Class Loader cont'd

Class Loader cont'd

How does it protect? Prevents malicious code from

interfering with benevolent code – namespace. Classes are loaded into its own namespace. No access to other classes outside of its own namespace.

It guards the borders of the trusted class libraries. Customizable.

Class Verifier

Checks the integrity of the class file to ensure no illegal bytecodes have been added

Uses built-in theorem prover to check integrity

Class Verifier

4 passes1. Class file is read into interpreter and

basic format of class file is checked2. Additional verification of the class file

without looking at the bytecodes3. Bytecode verification of each method4. Additional bytecode verification at

runtime

Security Manager

Defines which requests are allowed or disallowed through methods which can be overridden

Works hand-in-hand with the class loader to define the boundaries of the sandbox, i.e. what is allowed or disallowed.

Other Methods

ActiveX uses code signing and digital signature. Verified signatures from trusted source imply reliable ActiveX control.

Java too offer digital signature in addition to the sandbox.

Questions?