Java Applet Security Diana Dong CS 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

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 passes 1. Class file is read into interpreter and basic format of class file is checked 2. Additional verification of the class file without looking at the bytecodes 3. Bytecode verification of each method 4. 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?