# Using the Java SecurityManager with Tomcat

- Why use a SecurityManager?
- System Requirements
- Precautions
- Types of Permissions
- Tomcat SecurityManager setup with Unix
- What happens when the SecurityManager detects a Security violation?

### Why use a SecurityManager?

The Java SecurityManager is what allows a web browser to run an applet in its own sandbox to prevent untrusted code from accessing files on the local system, connecting to a host other than the one the applet was loaded from, etc.

In the same way the SecurityManager protects you from an untrusted applet running in your browser, use of a SecurityManager while running Tomcat can protect your server from trojan servlets, JSP's, JSP beans, and tag libraries. Or even inadvertent mistakes.

Imagine if someone who is authorized to publish JSP's on your site invadvertently included the following in their JSP:

>     <% System.exit(1); %>

Every time that JSP was executed by Tomcat, Tomcat would exit.

Using the Java SecurityManager is just one more line of defense a system administrator can use to keep the server secure and reliable.

### System Requirements

Use of the SecurityManager requires a JVM that supports JDK 1.2.

### Precautions

Implementation of a SecurityManager in Tomcat has not been fully tested to ensure the security of Tomcat. No special Permissions have been created to prevent access to internal Tomcat classes by JSP's, web applications, servlets, beans, or tag libraries. Make sure that you are satisfied with your SecurityManager configuration before allowing untrusted users to publish web applications, JSP's, servlets, beans, or tag libraries.

Still, running with a SecurityManager is definitely better than running without one.

### Types of Permissions

Permission classes are used to define what Permissions a class loaded by Tomcat will have. There are a number of Permission classes as part of the JDK and you can even create your own Permission class for use in your own web applications.

This is just a short summary of the System SecurityManager Permission classes applicable to Tomcat. Please refer to the JDK documentation for more information on using the below Permissions.

java.util.PropertyPermission
Controls read/write access to JVM properties such as java.home.

java.lang.RuntimePermission
Controls use of some System/Runtime functions like exit() and exec().

java.io.FilePermission
Controls read/write/execute access to files and directories.

java.net.SocketPermission
Controls use of network sockets.

java.net.NetPermission
Controls use of multicast network connections.

java.lang.reflect.ReflectPermission
Controls use of reflection to do class introspection.

java.security.SecurityPermission
Controls access to Security methods.

java.security.AllPermission
Allows access to all permissions, just as if you were running Tomcat without a SecurityManager.

### What happens when the SecurityManager detects a Security violation?

The JVM will throw an AccessControlException or a SecurityException when the SecurityManager detects a security policy violation.