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Background
> 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 file system, connecting to a host other than the one the applet was loaded from, and so on. 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, JSPs, JSP beans, and tag libraries. Or even inadvertent mistakes. Imagine if someone who is authorized to publish JSPs on your site inadvertently included the following in their JSP:
>     <% System.exit(1); %>
Every time this 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. WARNING - Implementation of a SecurityManager in Tomcat has not been fully tested or had a security audit. Make sure that you are satisfied with your SecurityManager configuration before allowing untrusted users to publish web applications, JSPs, servlets, beans, or tag libraries. However, running with a SecurityManager is definitely better than running without one.
Permissions
> Permission classes are used to define what Permissions a class loaded by Tomcat will have. There are a number of Permission classes that are a standard part of the JDK, and you can create your own Permission class for use in your own web applications. Both techniques are used in Tomcat 4.
> Standard Permissions
> This is just a short summary of the standard system SecurityManager Permission classes applicable to Tomcat. See http://java.sun.com/security/ for more information. 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.
> Tomcat Custom Permissions
> > Tomcat utilizes a custom permission class called org.apache.naming.JndiPermission. This permission controls read access to JNDI named file based resources. The permission name is the JNDI name and there are no actions. A trailing "*" can be used to do wild card matching for a JNDI named file resource when granting permission. For example, you might include the following in your policy file:
> >     permission  org.apache.naming.JndiPermission  "jndi://localhost/examples/*";
> A Permission entry like this is generated dynamically for each web application that is deployed, to allow it to read its own static resources but disallow it from using file access to read any other files (unless permissions for those files are explicitly granted).
Configuring Tomcat With A SecurityManager
> ### Policy File Format The security policies implemented by the Java SecurityManager are configured in the `$CATALINA_HOME/conf/catalina.policy` file. This file completely replaces the `java.policy` file present in your JDK system directories. The `catalina.policy` file can be edited by hand, or you can use the policytool application that comes with Java 1.2 or later. Entries in the `catalina.policy` file use the standard `java.policy` file format, as follows:
>     // Example policy file entry

>     grant [signedBy <signer>,] [codeBase <code source>] {
>       permission  <class>  [<name> [, <action list>]];
>     };
> The signedBy and codeBase entries are optional when granting permissions. Comment lines begin with "//" and end at the end of the current line. The `codeBase` is in the form of a URL, and for a file URL can use the `${java.home}` and `${catalina.home}` properties (which are expanded out to the directory paths defined for them by the `JAVA_HOME` and `CATALINA_HOME` environment variables). ### The Default Policy File The default `$CATALINA_HOME/conf/catalina.policy` file looks like this:
>     // ============================================================================
>     // catalina.corepolicy - Security Policy Permissions for Tomcat 4.0
>     //
>     // This file contains a default set of security policies to be enforced (by the
>     // JVM) when Catalina is executed with the "-security" option.  In addition
>     // to the permissions granted here, the following additional permissions are
>     // granted to the codebase specific to each web application:
>     //
>     // * Read access to the document root directory
>     //
>     // $Id: security-manager-howto.xml,v 1.1 2001/09/09 22:43:48 craigmcc Exp $
>     // ============================================================================

>     // ========== SYSTEM CODE PERMISSIONS =========================================

>     // These permissions apply to javac
>     grant codeBase "file:${java.home}/lib/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to all shared system extensions
>     grant codeBase "file:${java.home}/jre/lib/ext/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to javac when ${java.home] points at $JAVA_HOME/jre
>     grant codeBase "file:${java.home}/../lib/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to all shared system extensions when
>     // ${java.home} points at $JAVA_HOME/jre
>     grant codeBase "file:${java.home}/lib/ext/-" {
>             permission java.security.AllPermission;
>     };

>     // ========== CATALINA CODE PERMISSIONS =======================================

>     // These permissions apply to the server startup code
>     grant codeBase "file:${catalina.home}/bin/bootstrap.jar" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to the servlet API classes
>     // and those that are shared across all class loaders
>     // located in the "common" directory
>     grant codeBase "file:${catalina.home}/common/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to the container's core code, plus any additional
>     // libraries installed in the "server" directory
>     grant codeBase "file:${catalina.home}/server/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to the jasper page compiler
>     // located in the "jasper" directory.
>     grant codeBase "file:${catalina.home}/jasper/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to shared web application libraries
>     // including the Jasper runtime library installed in the "lib" directory
>     grant codeBase "file:${catalina.home}/lib/-" {
>             permission java.security.AllPermission;
>     };

>     // These permissions apply to shared web application classes
>     // located in the "classes" directory
>     grant codeBase "file:${catalina.home}/classes/-" {
>             permission java.security.AllPermission;
>     };

>     // ========== WEB APPLICATION PERMISSIONS =====================================

>     // These permissions are granted by default to all web applications
>     // In addition, a web application will be given a read FilePermission
>     // and JndiPermission for all files and directories in its document root.
>     grant {
>             // Required for JNDI lookup of named JDBC DataSource's and
>             // javamail named MimePart DataSource used to send mail
>             permission java.util.PropertyPermission "java.home", "read";
>             permission java.util.PropertyPermission "java.naming.*", "read";
>             permission java.util.PropertyPermission "javax.sql.*", "read";

>             // OS Specific properties to allow read access
>     	permission java.util.PropertyPermission "os.name", "read";
>     	permission java.util.PropertyPermission "os.version", "read";
>     	permission java.util.PropertyPermission "os.arch", "read";
>     	permission java.util.PropertyPermission "file.separator", "read";
>     	permission java.util.PropertyPermission "path.separator", "read";
>     	permission java.util.PropertyPermission "line.separator", "read";

>             // JVM properties to allow read access
>             permission java.util.PropertyPermission "java.version", "read";
>             permission java.util.PropertyPermission "java.vendor", "read";
>             permission java.util.PropertyPermission "java.vendor.url", "read";
>             permission java.util.PropertyPermission "java.class.version", "read";
>     	permission java.util.PropertyPermission "java.specification.version", "read";
>     	permission java.util.PropertyPermission "java.specification.vendor", "read";
>     	permission java.util.PropertyPermission "java.specification.name", "read";

>     	permission java.util.PropertyPermission "java.vm.specification.version", "read";
>     	permission java.util.PropertyPermission "java.vm.specification.vendor", "read";
>     	permission java.util.PropertyPermission "java.vm.specification.name", "read";
>     	permission java.util.PropertyPermission "java.vm.version", "read";
>     	permission java.util.PropertyPermission "java.vm.vendor", "read";
>     	permission java.util.PropertyPermission "java.vm.name", "read";

>             // Required for getting BeanInfo
>             permission java.lang.RuntimePermission "accessClassInPackage.sun.beans.*";

>     	// Allow read of JAXP compliant XML parser debug
>     	permission java.util.PropertyPermission "jaxp.debug", "read";
>     };

>     // You can assign additional permissions to particular web applications by
>     // adding additional "grant" entries here, based on the code base for that
>     // application, /WEB-INF/classes/, or /WEB-INF/lib/ jar files.
>     //
>     // Different permissions can be granted to JSP pages, classes loaded from
>     // the /WEB-INF/classes/ directory, all jar files in the /WEB-INF/lib/
>     // directory, or even to individual jar files in the /WEB-INF/lib/ directory.
>     //
>     // For instance, assume that the standard "examples" application
>     // included a JDBC driver that needed to establish a network connection to the
>     // corresponding database and used the scrape taglib to get the weather from
>     // the NOAA web server.  You might create a "grant" entries like this:
>     //
>     // The permissions granted to the context root directory apply to JSP pages.
>     // grant codeBase "file:${catalina.home}/webapps/examples/-" {
>     //      permission java.net.SocketPermission "dbhost.mycompany.com:5432", "connect";
>     //      permission java.net.SocketPermission "*.noaa.gov:80", "connect";
>     // };
>     //
>     // The permissions granted to the context WEB-INF/classes directory
>     // grant codeBase "file:${catalina.home}/webapps/examples/WEB-INF/classes/-" {
>     // };
>     //
>     // The permission granted to your JDBC driver
>     // grant codeBase "file:${catalina.home}/webapps/examples/WEB-INF/lib/driver.jar!/-" {
>     //      permission java.net.SocketPermission "dbhost.mycompany.com:5432", "connect";
>     // };
>     // The permission granted to the scrape taglib
>     // grant codeBase "file:${catalina.home}/webapps/examples/WEB-INF/lib/scrape.jar!/-" {
>     //      permission java.net.SocketPermission "*.noaa.gov:80", "connect";
>     // };
> ### Starting Tomcat With A SecurityManager Once you have configured the `catalina.policy` file for use with a SecurityManager, Tomcat can be started with a SecurityManager in place by using the "-security" option:
>     $CATALINA_HOME/bin/catalina.sh start -security    (Unix)
>     %CATALINA_HOME%\bin\catalina start -security      (Windows)
Troubleshooting
> If your web application attempts to execute an operation that is prohibited by lack of a required Permission, it will throw an `AccessControLException` or a `SecurityException` when the SecurityManager detects the violation. Debugging the permission that is missing can be challenging, and one option is to turn on debug output of all security decisions that are made during execution. This is done by setting a system property before starting Tomcat. The easiest way to do this is via the `CATALINA_OPTS` environment variable. Execute this command:
>     export CATALINA_OPTS=-Djava.security.debug=all    (Unix)
>     set CATALINA_OPTS=-Djava.security.debug=all       (Windows)
before starting Tomcat. WARNING - This will generate many megabytes of output! However, it can help you track down problems by searching for the word "FAILED" and determining which permission was being checked for. See the Java security documentation for more options that you can specify here as well.
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