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Scripting and the Java Security Manager

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Scripting and the Java Security Manager

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Elasticsearch runs with the Java Security Manager enabled by default. The security policy in Elasticsearch locks down the permissions granted to each class to the bare minimum required to operate. The benefit of doing this is that it severely limits the attack vectors available to a hacker.

Restricting permissions is particularly important with scripting languages like Groovy and Javascript which are designed to do anything that can be done in Java itself, including writing to the file system, opening sockets to remote servers, etc.

Script Classloader Whitelist

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Scripting languages are only allowed to load classes which appear in a hardcoded whitelist that can be found in org.elasticsearch.script.ClassPermission.

In a script, attempting to load a class that does not appear in the whitelist may result in a ClassNotFoundException, for instance this script:

GET _search
{
  "script_fields": {
    "the_hour": {
      "script": "use(java.math.BigInteger); new BigInteger(1)"
    }
  }
}

will return the following exception:

{
  "reason": {
    "type": "script_exception",
    "reason": "failed to run inline script [use(java.math.BigInteger); new BigInteger(1)] using lang [groovy]",
    "caused_by": {
      "type": "no_class_def_found_error",
      "reason": "java/math/BigInteger",
      "caused_by": {
        "type": "class_not_found_exception",
        "reason": "java.math.BigInteger"
      }
    }
  }
}

However, classloader issues may also result in more difficult to interpret exceptions. For instance, this script:

use(groovy.time.TimeCategory); new Date(123456789).format('HH')

Returns the following exception:

{
  "reason": {
    "type": "script_exception",
    "reason": "failed to run inline script [use(groovy.time.TimeCategory); new Date(123456789).format('HH')] using lang [groovy]",
    "caused_by": {
      "type": "missing_property_exception",
      "reason": "No such property: groovy for class: 8d45f5c1a07a1ab5dda953234863e283a7586240"
    }
  }
}

Dealing with Java Security Manager issues

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If you encounter issues with the Java Security Manager, you have three options for resolving these issues:

Fix the security problem

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The safest and most secure long term solution is to change the code causing the security issue. We recognise that this may take time to do correctly and so we provide the following two alternatives.

Disable the Java Security Manager

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Deprecated in 2.2.0.

The ability to disable the Java Security Manager will be removed in a future version

You can disable the Java Security Manager entirely with the security.manager.enabled command line flag:

./bin/elasticsearch --security.manager.enabled false

This disables the Security Manager entirely and makes Elasticsearch much more vulnerable to attacks! It is an option that should only be used in the most urgent of situations and for the shortest amount of time possible. Optional security is not secure at all because it will be disabled and leave the system vulnerable. This option will be removed in a future version.

Customising the classloader whitelist

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The classloader whitelist can be customised by tweaking the local Java Security Policy either:

system wide: $JAVA_HOME/lib/security/java.policy,
for just the elasticsearch user: /home/elasticsearch/.java.policy, or

from a file specified in the JAVA_OPTS environment variable with -Djava.security.policy=someURL:

export JAVA_OPTS="${JAVA_OPTS} -Djava.security.policy=file:///path/to/my.policy`
./bin/elasticsearch

Permissions may be granted at the class, package, or global level. For instance:

grant {
    permission org.elasticsearch.script.ClassPermission "java.util.Base64"; // allow class
    permission org.elasticsearch.script.ClassPermission "java.util.*"; // allow package
    permission org.elasticsearch.script.ClassPermission "*"; // allow all (disables filtering basically)
};

Here is an example of how to enable the groovy.time.TimeCategory class:

grant {
    permission org.elasticsearch.script.ClassPermission "java.lang.Class";
    permission org.elasticsearch.script.ClassPermission "groovy.time.TimeCategory";
};

Before adding classes to the whitelist, consider the security impact that it will have on Elasticsearch. Do you really need an extra class or can your code be rewritten in a more secure way?

It is quite possible that we have not whitelisted a generically useful and safe class. If you have a class that you think should be whitelisted by default, please open an issue on GitHub and we will consider the impact of doing so.

See http://docs.oracle.com/javase/7/docs/technotes/guides/security/PolicyFiles.html for more information.

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