From version 5.0 onward, Shield is part of X-Pack. For more information, see Securing the Elastic Stack.

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esusers - Internal File Based Authentication

The esusers realm is the default Shield realm. The esusers realm enables the registration of users, passwords for those users, and associates those users with roles. The esusers command-line tool assists with the registration and administration of users.

`esusers` Realm Settings

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Like all other realms, the esusers realm is configured under the shield.authc.realms settings namespace in the elasticsearch.yml file. The following snippet shows an example of such configuration:

Example esusers Realm Configuration.

shield:
  authc:
    realms:
      default:
        type: esusers
        order: 0

Table 1. esusers Realm Settings

Setting	Required	Description
`type`	yes	Indicates the realm type and must be set to `esusers`.
`order`	no	Indicates the priority of this realm within the realm chain. Realms with lower order will be consulted first. Although not required, it is highly recommended to explicitly set this value when multiple realms are configured. Defaults to `Integer.MAX_VALUE`.
`enabled`	no	Indicates whether this realm is enabled/disabled. Provides an easy way to disable realms in the chain without removing their configuration. Defaults to `true`.
`files.users`	no	Points to the location of the `users` file where the users and their passwords are stored. Defaults to `users` file under shield’s config directory.
`files.users_roles`	no	Points to the location of the `users_roles` file where the users and their roles are stored. Defaults to `users_roles` file under shield’s config directory.
`cache.ttl`	no	Specified the time-to-live for cached user entries (a user and its credentials will be cached for this configured period of time). Defaults to `20m` (use the standard elasticsearch time units).
`cache.max_users`	no	Specified the maximum number of user entries that can live in the cache at a given time. Defaults to 100,000.
`cache.hash_algo`	no	(Expert Setting) Specifies the hashing algorithm that will be used for the in-memory cached user credentials (see here for possible values).

When no realms are explicitly configured in elasticsearch.yml, a default realm chain will be created that holds a single esusers realm. If you wish to only work with esusers realm and you’re satisfied with the default files paths, there is no real need to add the above configuration.

The `esusers` Command Line Tool

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The esusers command line tool is located under Shield’s bin directory and enables several administrative tasks for managing users:

Adding Users

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The esusers useradd command adds a user to your cluster.

To ensure that Elasticsearch can read the user and role information at startup, run esusers useradd as the same user you use to run Elasticsearch. Running the command as root or some other user will update the permissions for the users and users_roles files and prevent Elasticsearch from accessing them.

esusers useradd <username>

A username must be at least 1 character and no longer than 30 characters. The first character must be a letter (a-z or A-Z) or an underscore (_). Subsequent characters can be letters, underscores (_), digits (0-9), or any of the following symbols @, - or $

You can specify the user’s password at the command line with the -p option. When this option is absent, the esusers command prompts you for the password. Omit the -p option to keep plaintext passwords out of the terminal session’s command history.

esusers useradd <username> -p <secret>

Passwords must be at least 6 characters long.

You can define a user’s roles with the -r parameter. This parameter accepts a comma-separated list of role names to associate with the user.

esusers useradd <username> -r <comma-separated list of role names>

The following example adds a new user named jacknich to the esusers realm. The password for this user is theshining, and this user is associated with the logstash and marvel roles.

esusers useradd jacknich -p theshining -r logstash,marvel

For valid role names please see Role Definitions.

Listing Users

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The esusers list command lists the users registered in the esusers realm, as in the following example:

esusers list
rdeniro        : admin
alpacino       : power_user
jacknich       : marvel,logstash

Users are in the left-hand column and their corresponding roles are listed in the right-hand column.

Listing Specific Users

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The esusers list <username> command lists a specific user. Use this command to verify that a user has been successfully added to the cluster.

esusers list jacknich
jacknich       : marvel,logstash

Changing Users' Passwords

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The esusers passwd command enables you to reset a user’s password. You can specify the new password directly with the -p option. When -p option is omitted, the tool will prompt you to enter and confirm a password in interactive mode.

esusers passwd <username>

esusers passwd <username> -p <password>

Changing Users' Roles

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The esusers roles command manages the roles associated to a particular user. The -a option adds a comma-separated list of roles to a user. The -r option removes a comma-separated list of roles from a user. You can combine adding and removing roles within the same command to change a user’s roles.

esusers roles <username> -a <commma-separate list of roles> -r <commma-separate list of roles>

The following command removes the logstash and marvel roles from user jacknich, as well as adding the user role:

esusers roles jacknich -r logstash,marvel -a user

Listing the user displays the new role assignment:

esusers list jacknich
jacknich       : user

Deleting Users

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The esusers userdel command deletes a user.

userdel <username>

How `esusers` Works

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The esusers tool manipulates two files, users and users_roles, in Shield’s config directory. These two files store all user data for the esusers realm and are read by Shield on startup.

By default, Shield checks these files for changes every 5 seconds. You can change this default behavior by changing the value of the watcher.interval.high setting in the elasticsearch.yml file.

These files are managed locally by the node and are not managed globally by the cluster. This means that with a typical multi-node cluster, the exact same changes need to be applied on each and every node in the cluster.

A safer approach would be to apply the change on one of the nodes and have the users and users_roles files distributed/copied to all other nodes in the cluster (either manually or using a configuration management system such as Puppet or Chef).

While it is possible to modify these files directly using any standard text editor, we strongly recommend using the esusers command-line tool to apply the required changes.

The `users` File

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The users file stores all the users and their passwords. The format of the users file follows the format of an htpasswd file from a standard Apache webserver, where each line contains a single user entry that holds its username and its hashed password.

rdeniro:$2a$10$BBJ/ILiyJ1eBTYoRKxkqbuDEdYECplvxnqQ47uiowE7yGqvCEgj9W
alpacino:$2a$10$cNwHnElYiMYZ/T3K4PvzGeJ1KbpXZp2PfoQD.gfaVdImnHOwIuBKS
jacknich:$2a$10$GYUNWyABV/Ols/.bcwxuBuuaQzV6WIauW6RdboojxcixBq3LtI3ni

The esusers command-line tool uses bcrypt to hash the password by default. All of the htpasswd hash algorithms are available as an option.

The `users_roles` File

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The users_roles file stores the roles associated with the users, as in the following example:

admin:rdeniro
power_user:alpacino,jacknich
user:jacknich

Each row maps a role to a comma-separated list of all the users that are associated with that role.

User Cache

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The user credentials are not stored on disk in clear text. The esusers creates a bcrypt hashes of the passwords and stores those. bcrypt is considered to be highly secured hash and by default it uses 10 rounds to generate the salts it hashes with. While highly secured, it is also relatively slow. For this reason, Shield also introduce an in-memory cache over the esusers store. This cache can use a different hashing algorithm for storing the passwords in memeory. The default hashing algorithm that is used is ssha256 - a salted SHA-256 algorithm.

We’ve seen in the table above that the cache characteristics can be configured. The following table describes the different hash algorithm that can be set:

Table 2. Cache hash algorithms

Algorithm	Description
`ssha256`	Uses a salted `SHA-256` algorithm (default).
`md5`	Uses `MD5` algorithm.
`sha1`	Uses `SHA1` algorithm.
`bcrypt`	Uses `bcrypt` algorithm with salt generated in 10 rounds.
`bcrypt4`	Uses `bcrypt` algorithm with salt generated in 4 rounds.
`bcrypt5`	Uses `bcrypt` algorithm with salt generated in 5 rounds.
`bcrypt6`	Uses `bcrypt` algorithm with salt generated in 6 rounds.
`bcrypt7`	Uses `bcrypt` algorithm with salt generated in 7 rounds.
`bcrypt8`	Uses `bcrypt` algorithm with salt generated in 8 rounds.
`bcrypt9`	Uses `bcrypt` algorithm with salt generated in 9 rounds.
`sha2`	Uses `SHA2` algorithm.
`apr1`	Uses `apr1` algorithm (md5 crypt).
`noop`,`clear_text`	Doesn’t hash the credentials and keeps it in clear text in memory. CAUTION: keeping clear text is considered insecure and can be compromised at the OS level (e.g. memory dumps and `ptrace`).

Cache Eviction API

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Shield exposes an API to force cached user eviction. The following example, evicts all users from the ldap1 realm:

$ curl -XPOST 'http://localhost:9200/_shield/realm/esusers/_cache/clear'

It is also possible to evict specific users:

$ curl -XPOST 'http://localhost:9200/_shield/realm/esusers/_cache/clear?usernames=rdeniro,alpacino'

Multiple realms can also be specified using comma-delimited list:

$ curl -XPOST 'http://localhost:9200/_shield/realm/esusers,ldap1/_cache/clear'

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esusers - Internal File Based Authentication