Scripting and securityedit

While Elasticsearch contributors make every effort to prevent scripts from running amok, security is something best done in layers because all software has bugs and it is important to minimize the risk of failure in any security layer. Find below rules of thumb for how to keep Elasticsearch from being a vulnerability.

Do not run as rootedit

First and foremost, never run Elasticsearch as the root user as this would allow any successful effort to circumvent the other security layers to do anything on your server. Elasticsearch will refuse to start if it detects that it is running as root but this is so important that it is worth double and triple checking.

Do not expose Elasticsearch directly to usersedit

Do not expose Elasticsearch directly to users, instead have an application make requests on behalf of users. If this is not possible, have an application to sanitize requests from users. If that is not possible then have some mechanism to track which users did what. Understand that it is quite possible to write a _search that overwhelms Elasticsearch and brings down the cluster. All such searches should be considered bugs and the Elasticsearch contributors make an effort to prevent this but they are still possible.

Do not expose Elasticsearch directly to the Internetedit

Do not expose Elasticsearch to the Internet, instead have an application make requests on behalf of the Internet. Do not entertain the thought of having an application "sanitize" requests to Elasticsearch. Understand that it is possible for a sufficiently determined malicious user to write searches that overwhelm the Elasticsearch cluster and bring it down. For example:

Good: * Users type text into a search box and the text is sent directly to a Match Query, Match Phrase Query, Simple Query String Query, or any of the Suggesters. * Running a script with any of the above queries that was written as part of the application development process. * Running a script with params provided by users. * User actions makes documents with a fixed structure.

Bad: * Users can write arbitrary scripts, queries, _search requests. * User actions make documents with structure defined by users.

Do not weaken script security settingsedit

By default Elasticsearch will run inline, stored, and filesystem scripts for the builtin languages, namely the scripting language Painless, the template language Mustache, and the expression language Expressions. These ought to be safe to expose to trusted users and to your application servers because they have strong security sandboxes. The Elasticsearch committers do not support any non-sandboxed scripting languages and using any would be a poor choice because: 1. This drops a layer of security, leaving only Elasticsearch’s builtin security layers. 2. Non-sandboxed scripts have unchecked access to Elasticsearch’s internals and can cause all kinds of trouble if misused.

Other security layersedit

In addition to user privileges and script sandboxing Elasticsearch uses the Java Security Manager and native security tools as additional layers of security.

As part of its startup sequence Elasticsearch enables the Java Security Manager which limits the actions that can be taken by portions of the code. Painless uses this to limit the actions that generated Painless scripts can take, preventing them from being able to do things like write files and listen to sockets.

Elasticsearch uses seccomp in Linux, Seatbelt in macOS, and ActiveProcessLimit on Windows to prevent Elasticsearch from forking or executing other processes.

Below this we describe the security settings for scripts and how you can change from the defaults described above. You should be very, very careful when allowing more than the defaults. Any extra permissions weakens the total security of the Elasticsearch deployment.

Allowed script types settingedit

By default all script types are allowed to be executed. This can be modified using the setting script.allowed_types. Only the types specified as part of the setting will be allowed to be executed. To specify no types are allowed, set scripts.allowed_types to be none.

script.allowed_types: inline 

This will allow only inline scripts to be executed but not stored scripts (or any other types).

Allowed script contexts settingedit

By default all script contexts are allowed to be executed. This can be modified using the setting script.allowed_contexts. Only the contexts specified as part of the setting will be allowed to be executed. To specify no contexts are allowed, set scripts.allowed_contexts to be none.

script.allowed_contexts: search, update 

This will allow only search and update scripts to be executed but not aggs or plugin scripts (or any other contexts).