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      How To Install and Secure Redis on Debian 9


      Introduction

      Redis is an in-memory key-value store known for its flexibility, performance, and wide language support. This tutorial demonstrates how to install, configure, and secure Redis on a Debian 9 server.

      Prerequisites

      To complete this guide, you will need access to a Debian 9 server that has a non-root user with sudo privileges and a basic firewall configured. You can set this up by following our Initial Server Setup guide.

      When you are ready to begin, log in to your server as your sudo-enabled user and continue below.

      Step 1 — Installing and Configuring Redis

      In order to get the latest version of Redis, we will use apt to install it from the official Debian repositories.

      Update your local apt package cache and install Redis by typing:

      • sudo apt update
      • sudo apt install redis-server

      This will download and install Redis and its dependencies. Following this, there is one important configuration change to make in the Redis configuration file, which was generated automatically during the installation.

      Open this file with your preferred text editor:

      • sudo nano /etc/redis/redis.conf

      Inside the file, find the supervised directive. This directive allows you to declare an init system to manage Redis as a service, providing you with more control over its operation. The supervised directive is set to no by default. Since you are running Debian, which uses the systemd init system, change this to systemd:

      /etc/redis/redis.conf

      . . .
      
      # If you run Redis from upstart or systemd, Redis can interact with your
      # supervision tree. Options:
      #   supervised no      - no supervision interaction
      #   supervised upstart - signal upstart by putting Redis into SIGSTOP mode
      #   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
      #   supervised auto    - detect upstart or systemd method based on
      #                        UPSTART_JOB or NOTIFY_SOCKET environment variables
      # Note: these supervision methods only signal "process is ready."
      #       They do not enable continuous liveness pings back to your supervisor.
      supervised systemd
      
      . . .
      

      That’s the only change you need to make to the Redis configuration file at this point, so save and close it when you are finished. Then, reload the Redis service file to reflect the changes you made to the configuration file:

      • sudo systemctl restart redis

      With that, you’ve installed and configured Redis and it’s running on your machine. Before you begin using it, though, it’s prudent to first check whether Redis is functioning correctly.

      Step 2 — Testing Redis

      As with any newly-installed software, it’s a good idea to ensure that Redis is functioning as expected before making any further changes to its configuration. We will go over a handful of ways to check that Redis is working correctly in this step.

      Start by checking that the Redis service is running:

      • sudo systemctl status redis

      If it is running without any errors, this command will produce output similar to the following:

      Output

      ● redis-server.service - Advanced key-value store Loaded: loaded (/lib/systemd/system/redis-server.service; enabled; vendor preset: enabled) Active: active (running) since Wed 2018-09-05 20:19:44 UTC; 41s ago Docs: http://redis.io/documentation, man:redis-server(1) Process: 10829 ExecStopPost=/bin/run-parts --verbose /etc/redis/redis-server.post-down.d (code=exited, status=0/SUCCESS) Process: 10825 ExecStop=/bin/kill -s TERM $MAINPID (code=exited, status=0/SUCCESS) Process: 10823 ExecStop=/bin/run-parts --verbose /etc/redis/redis-server.pre-down.d (code=exited, status=0/SUCCESS) Process: 10842 ExecStartPost=/bin/run-parts --verbose /etc/redis/redis-server.post-up.d (code=exited, status=0/SUCCESS) Process: 10838 ExecStart=/usr/bin/redis-server /etc/redis/redis.conf (code=exited, status=0/SUCCESS) Process: 10834 ExecStartPre=/bin/run-parts --verbose /etc/redis/redis-server.pre-up.d (code=exited, status=0/SUCCESS) Main PID: 10841 (redis-server) Tasks: 3 (limit: 4915) CGroup: /system.slice/redis-server.service └─10841 /usr/bin/redis-server 127.0.0.1:6379 . . .

      Here, you can see that Redis is running and is already enabled, meaning that it is set to start up every time the server boots.

      Note: This setting is desirable for many common use cases of Redis. If, however, you prefer to start up Redis manually every time your server boots, you can configure this with the following command:

      • sudo systemctl disable redis

      To test that Redis is functioning correctly, connect to the server using the command-line client:

      In the prompt that follows, test connectivity with the ping command:

      Output

      PONG

      This output confirms that the server connection is still alive. Next, check that you’re able to set keys by running:

      Output

      OK

      Retrieve the value by typing:

      Assuming everything is working, you will be able to retrieve the value you stored:

      Output

      "It's working!"

      After confirming that you can fetch the value, exit the Redis prompt to get back to the shell:

      As a final test, we will check whether Redis is able to persist data even after it’s been stopped or restarted. To do this, first restart the Redis instance:

      • sudo systemctl restart redis

      Then connect with the command-line client once again and confirm that your test value is still available:

      The value of your key should still be accessible:

      Output

      "It's working!"

      Exit out into the shell again when you are finished:

      With that, your Redis installation is fully operational and ready for you to use. However, some of its default configuration settings are insecure and provide malicious actors with opportunities to attack and gain access to your server and its data. The remaining steps in this tutorial cover methods for mitigating these vulnerabilities, as prescribed by the official Redis website. Although these steps are optional and Redis will still function if you choose not to follow them, it is strongly recommended that you complete them in order to harden your system’s security.

      Step 3 — Binding to localhost

      By default, Redis is only accessible from localhost. However, if you installed and configured Redis by following a different tutorial than this one, you might have updated the configuration file to allow connections from anywhere. This is not as secure as binding to localhost.

      To correct this, open the Redis configuration file for editing:

      • sudo nano /etc/redis/redis.conf

      Locate this line and make sure it is uncommented (remove the # if it exists):

      /etc/redis/redis.conf

      bind 127.0.0.1
      

      Save and close the file when finished (press CTRL + X, Y, then ENTER).

      Then, restart the service to ensure that systemd reads your changes:

      • sudo systemctl restart redis

      To check that this change has gone into effect, run the following netstat command:

      • sudo netstat -lnp | grep redis

      Output

      tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 10959/redis-server

      This output shows that the redis-server program is bound to localhost (127.0.0.1), reflecting the change you just made to the configuration file. If you see another IP address in that column (0.0.0.0, for example), then you should double check that you uncommented the correct line and restart the Redis service again.

      Now that your Redis installation is only listening in on localhost, it will be more difficult for malicious actors to make requests or gain access to your server. However, Redis isn’t currently set to require users to authenticate themselves before making changes to its configuration or the data it holds. To remedy this, Redis allows you to require users to authenticate with a password before making changes via the Redis client (redis-cli).

      Step 4 — Configuring a Redis Password

      Configuring a Redis password enables one of its two built-in security features — the auth command, which requires clients to authenticate to access the database. The password is configured directly in Redis's configuration file, /etc/redis/redis.conf, so open that file again with your preferred editor:

      • sudo nano /etc/redis/redis.conf

      Scroll to the SECURITY section and look for a commented directive that reads:

      /etc/redis/redis.conf

      # requirepass foobared
      

      Uncomment it by removing the #, and change foobared to a secure password.

      Note: Above the requirepass directive in the redis.conf file, there is a commented warning:

      # Warning: since Redis is pretty fast an outside user can try up to
      # 150k passwords per second against a good box. This means that you should
      # use a very strong password otherwise it will be very easy to break.
      #
      

      Thus, it’s important that you specify a very strong and very long value as your password. Rather than make up a password yourself, you can use the openssl command to generate a random one, as in the following example. By piping the output of the first command to the second openssl command, as shown here, it will remove any line breaks produced by that the first command:

      • openssl rand 60 | openssl base64 -A

      Your output should look something like:

      Output

      RBOJ9cCNoGCKhlEBwQLHri1g+atWgn4Xn4HwNUbtzoVxAYxkiYBi7aufl4MILv1nxBqR4L6NNzI0X6cE

      After copying and pasting the output of that command as the new value for requirepass, it should read:

      /etc/redis/redis.conf

      requirepass RBOJ9cCNoGCKhlEBwQLHri1g+atWgn4Xn4HwNUbtzoVxAYxkiYBi7aufl4MILv1nxBqR4L6NNzI0X6cE

      After setting the password, save and close the file, then restart Redis:

      • sudo systemctl restart redis.service

      To test that the password works, access the Redis command line:

      The following shows a sequence of commands used to test whether the Redis password works. The first command tries to set a key to a value before authentication:

      That won't work because you didn’t authenticate, so Redis returns an error:

      Output

      (error) NOAUTH Authentication required.

      The next command authenticates with the password specified in the Redis configuration file:

      Redis acknowledges:

      Output

      OK

      After that, running the previous command again will succeed:

      Output

      OK

      get key1 queries Redis for the value of the new key.

      Output

      "10"

      After confirming that you’re able to run commands in the Redis client after authenticating, you can exit the redis-cli:

      Next, we'll look at renaming Redis commands which, if entered by mistake or by a malicious actor, could cause serious damage to your machine.

      Step 5 — Renaming Dangerous Commands

      The other security feature built into Redis involves renaming or completely disabling certain commands that are considered dangerous.

      When run by unauthorized users, such commands can be used to reconfigure, destroy, or otherwise wipe your data. Like the authentication password, renaming or disabling commands is configured in the same SECURITY section of the /etc/redis/redis.conf file.

      Some of the commands that are considered dangerous include: FLUSHDB, FLUSHALL, KEYS, PEXPIRE, DEL, CONFIG, SHUTDOWN, BGREWRITEAOF, BGSAVE, SAVE, SPOP, SREM, RENAME, and DEBUG. This is not a comprehensive list, but renaming or disabling all of the commands in that list is a good starting point for enhancing your Redis server’s security.

      Whether you should disable or rename a command depends on your specific needs or those of your site. If you know you will never use a command that could be abused, then you may disable it. Otherwise, it might be in your best interest to rename it.

      To enable or disable Redis commands, open the configuration file once more:

      • sudo nano /etc/redis/redis.conf

      Warning: The following steps showing how to disable and rename commands are examples. You should only choose to disable or rename the commands that make sense for you. You can review the full list of commands for yourself and determine how they might be misused at redis.io/commands.

      To disable a command, simply rename it to an empty string (signified by a pair of quotation marks with no characters between them), as shown below:

      /etc/redis/redis.conf

      . . .
      # It is also possible to completely kill a command by renaming it into
      # an empty string:
      #
      rename-command FLUSHDB ""
      rename-command FLUSHALL ""
      rename-command DEBUG ""
      . . .
      

      To rename a command, give it another name as shown in the examples below. Renamed commands should be difficult for others to guess, but easy for you to remember:

      /etc/redis/redis.conf

      . . .
      # rename-command CONFIG ""
      rename-command SHUTDOWN SHUTDOWN_MENOT
      rename-command CONFIG ASC12_CONFIG
      . . .
      

      Save your changes and close the file.

      After renaming a command, apply the change by restarting Redis:

      • sudo systemctl restart redis

      To test the new command, enter the Redis command line:

      Then, authenticate:

      Output

      OK

      Let’s assume that you renamed the CONFIG command to ASC12_CONFIG, as in the preceding example. First, try using the original CONFIG command. It should fail, because you’ve renamed it:

      Output

      (error) ERR unknown command 'config'

      Calling the renamed command, however, will be successful. It is not case-sensitive:

      • asc12_config get requirepass

      Output

      1) "requirepass" 2) "your_redis_password"

      Finally, you can exit from redis-cli:

      Note that if you're already using the Redis command line and then restart Redis, you'll need to re-authenticate. Otherwise, you'll get this error if you type a command:

      Output

      NOAUTH Authentication required.

      Regarding the practice of renaming commands, there's a cautionary statement at the end of the SECURITY section in /etc/redis/redis.conf which reads:

      Please note that changing the name of commands that are logged into the AOF file or transmitted to slaves may cause problems.

      Note: The Redis project chooses to use the terms “master” and “slave” while DigitalOcean generally prefers alternative descriptors. In order to avoid confusion we’ve chosen to use the terms used in the Redis documentation here.

      That means if the renamed command is not in the AOF file, or if it is but the AOF file has not been transmitted to slaves, then there should be no problem.

      So, keep that in mind when you're trying to rename commands. The best time to rename a command is when you're not using AOF persistence, or right after installation, that is, before your Redis-using application has been deployed.

      When you're using AOF and dealing with a master-slave installation, consider this answer from the project's GitHub issue page. The following is a reply to the author's question:

      The commands are logged to the AOF and replicated to the slave the same way they are sent, so if you try to replay the AOF on an instance that doesn't have the same renaming, you may face inconsistencies as the command cannot be executed (same for slaves).

      Thus, the best way to handle renaming in cases like that is to make sure that renamed commands are applied to all instances in master-slave installations.

      Conclusion

      In this tutorial, you installed and configured Redis, validated that your Redis installation is functioning correctly, and used its built-in security features to make it less vulnerable to attacks from malicious actors.

      Keep in mind that once someone is logged in to your server, it's very easy to circumvent the Redis-specific security features we've put in place. Therefore, the most important security feature on your Redis server is your firewall (which you configured if you followed the prerequisite Initial Server Setup tutorial), as this makes it extremely difficult for malicious actors to jump that fence.



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