[[modules-scripting-security]] === Scripting and security While Elasticsearch contributors make every effort to prevent scripts from running amok, security is something best done in https://en.wikipedia.org/wiki/Defense_in_depth_(computing)[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. [float] === Do not run as root 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. [float] === Do not expose Elasticsearch directly to users 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, `_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. [float] === Do not expose Elasticsearch directly to the Internet 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 <<query-dsl-match-query>>, <<query-dsl-match-query-phrase>>, <<query-dsl-simple-query-string-query>>, or any of the <<search-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. [float] [[modules-scripting-other-layers]] === Other security layers In addition to user privileges and script sandboxing Elasticsearch uses the http://www.oracle.com/technetwork/java/seccodeguide-139067.html[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 https://en.wikipedia.org/wiki/Seccomp[seccomp] in Linux, https://www.chromium.org/developers/design-documents/sandbox/osx-sandboxing-design[Seatbelt] in macOS, and https://msdn.microsoft.com/en-us/library/windows/desktop/ms684147[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-setting]] [float] === Allowed script types setting 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 `script.allowed_types` to be `none`. [source,yaml] ---- script.allowed_types: inline <1> ---- <1> This will allow only inline scripts to be executed but not stored scripts (or any other types). [[allowed-script-contexts-setting]] [float] === Allowed script contexts setting 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 `script.allowed_contexts` to be `none`. [source,yaml] ---- script.allowed_contexts: search, update <1> ---- <1> This will allow only search and update scripts to be executed but not aggs or plugin scripts (or any other contexts).