This is the multi-page printable view of this section. Click here to print.

Return to the regular view of this page.

Redis security

Security model and features in Redis

1: ACL
2: TLS

This document provides an introduction to the topic of security from the point of view of Redis. It covers the access control provided by Redis, code security concerns, attacks that can be triggered from the outside by selecting malicious inputs, and other similar topics.

For security-related contacts, open an issue on GitHub, or when you feel it is really important to preserve the security of the communication, use the GPG key at the end of this document.

Security model

Redis is designed to be accessed by trusted clients inside trusted environments. This means that usually it is not a good idea to expose the Redis instance directly to the internet or, in general, to an environment where untrusted clients can directly access the Redis TCP port or UNIX socket.

For instance, in the common context of a web application implemented using Redis as a database, cache, or messaging system, the clients inside the front-end (web side) of the application will query Redis to generate pages or to perform operations requested or triggered by the web application user.

In this case, the web application mediates access between Redis and untrusted clients (the user browsers accessing the web application).

In general, untrusted access to Redis should always be mediated by a layer implementing ACLs, validating user input, and deciding what operations to perform against the Redis instance.

Network security

Access to the Redis port should be denied to everybody but trusted clients in the network, so the servers running Redis should be directly accessible only by the computers implementing the application using Redis.

In the common case of a single computer directly exposed to the internet, such as a virtualized Linux instance (Linode, EC2, ...), the Redis port should be firewalled to prevent access from the outside. Clients will still be able to access Redis using the loopback interface.

Note that it is possible to bind Redis to a single interface by adding a line like the following to the redis.conf file:

bind 127.0.0.1

Failing to protect the Redis port from the outside can have a big security impact because of the nature of Redis. For instance, a single FLUSHALL command can be used by an external attacker to delete the whole data set.

Protected mode

Unfortunately, many users fail to protect Redis instances from being accessed from external networks. Many instances are simply left exposed on the internet with public IPs. Since version 3.2.0, Redis enters a special mode called protected mode when it is executed with the default configuration (binding all the interfaces) and without any password in order to access it. In this mode, Redis only replies to queries from the loopback interfaces, and replies to clients connecting from other addresses with an error that explains the problem and how to configure Redis properly.

We expect protected mode to seriously decrease the security issues caused by unprotected Redis instances executed without proper administration. However, the system administrator can still ignore the error given by Redis and disable protected mode or manually bind all the interfaces.

Authentication

While Redis does not try to implement Access Control, it provides a tiny layer of optional authentication that is turned on by editing the redis.conf file.

When the authorization layer is enabled, Redis will refuse any query by unauthenticated clients. A client can authenticate itself by sending the AUTH command followed by the password.

The password is set by the system administrator in clear text inside the redis.conf file. It should be long enough to prevent brute force attacks for two reasons:

Redis is very fast at serving queries. Many passwords per second can be tested by an external client.
The Redis password is stored in the redis.conf file and inside the client configuration. Since the system administrator does not need to remember it, the password can be very long.

The goal of the authentication layer is to optionally provide a layer of redundancy. If firewalling or any other system implemented to protect Redis from external attackers fail, an external client will still not be able to access the Redis instance without knowledge of the authentication password.

Since the AUTH command, like every other Redis command, is sent unencrypted, it does not protect against an attacker that has enough access to the network to perform eavesdropping.

TLS support

Redis has optional support for TLS on all communication channels, including client connections, replication links, and the Redis Cluster bus protocol.

Disallowing specific commands

It is possible to disallow commands in Redis or to rename them as an unguessable name, so that normal clients are limited to a specified set of commands.

For instance, a virtualized server provider may offer a managed Redis instance service. In this context, normal users should probably not be able to call the Redis CONFIG command to alter the configuration of the instance, but the systems that provide and remove instances should be able to do so.

In this case, it is possible to either rename or completely shadow commands from the command table. This feature is available as a statement that can be used inside the redis.conf configuration file. For example:

rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52

In the above example, the CONFIG command was renamed into an unguessable name. It is also possible to completely disallow it (or any other command) by renaming it to the empty string, like in the following example:

rename-command CONFIG ""

Attacks triggered by malicious inputs from external clients

There is a class of attacks that an attacker can trigger from the outside even without external access to the instance. For example, an attacker might insert data into Redis that triggers pathological (worst case) algorithm complexity on data structures implemented inside Redis internals.

An attacker could supply, via a web form, a set of strings that are known to hash to the same bucket in a hash table in order to turn the O(1) expected time (the average time) to the O(N) worst case. This can consume more CPU than expected and ultimately cause a Denial of Service.

To prevent this specific attack, Redis uses a per-execution, pseudo-random seed to the hash function.

Redis implements the SORT command using the qsort algorithm. Currently, the algorithm is not randomized, so it is possible to trigger a quadratic worst-case behavior by carefully selecting the right set of inputs.

String escaping and NoSQL injection

The Redis protocol has no concept of string escaping, so injection is impossible under normal circumstances using a normal client library. The protocol uses prefixed-length strings and is completely binary safe.

Since Lua scripts executed by the EVAL and EVALSHA commands follow the same rules, those commands are also safe.

While it would be a strange use case, the application should avoid composing the body of the Lua script from strings obtained from untrusted sources.

Code security

In a classical Redis setup, clients are allowed full access to the command set, but accessing the instance should never result in the ability to control the system where Redis is running.

Internally, Redis uses all the well-known practices for writing secure code to prevent buffer overflows, format bugs, and other memory corruption issues. However, the ability to control the server configuration using the CONFIG command allows the client to change the working directory of the program and the name of the dump file. This allows clients to write RDB Redis files to random paths. This is a security issue that may lead to the ability to compromise the system and/or run untrusted code as the same user as Redis is running.

Redis does not require root privileges to run. It is recommended to run it as an unprivileged redis user that is only used for this purpose.

GPG key

1 - ACL

Redis access control list

The Redis ACL, short for Access Control List, is the feature that allows certain connections to be limited in terms of the commands that can be executed and the keys that can be accessed. The way it works is that, after connecting, a client is required to provide a username and a valid password to authenticate. If authentication succeeded, the connection is associated with a given user and the limits the user has. Redis can be configured so that new connections are already authenticated with a "default" user (this is the default configuration). Configuring the default user has, as a side effect, the ability to provide only a specific subset of functionalities to connections that are not explicitly authenticated.

In the default configuration, Redis 6 (the first version to have ACLs) works exactly like older versions of Redis. Every new connection is capable of calling every possible command and accessing every key, so the ACL feature is backward compatible with old clients and applications. Also the old way to configure a password, using the requirepass configuration directive, still works as expected. However, it now sets a password for the default user.

The Redis AUTH command was extended in Redis 6, so now it is possible to use it in the two-arguments form:

AUTH <username> <password>

Here's an example of the old form:

AUTH <password>

What happens is that the username used to authenticate is "default", so just specifying the password implies that we want to authenticate against the default user. This provides backward compatibility.

When ACLs are useful

Before using ACLs, you may want to ask yourself what's the goal you want to accomplish by implementing this layer of protection. Normally there are two main goals that are well served by ACLs:

You want to improve security by restricting the access to commands and keys, so that untrusted clients have no access and trusted clients have just the minimum access level to the database in order to perform the work needed. For instance, certain clients may just be able to execute read only commands.
You want to improve operational safety, so that processes or humans accessing Redis are not allowed to damage the data or the configuration due to software errors or manual mistakes. For instance, there is no reason for a worker that fetches delayed jobs from Redis to be able to call the FLUSHALL command.

Another typical usage of ACLs is related to managed Redis instances. Redis is often provided as a managed service both by internal company teams that handle the Redis infrastructure for the other internal customers they have, or is provided in a software-as-a-service setup by cloud providers. In both setups, we want to be sure that configuration commands are excluded for the customers.

Configure ACLs with the ACL command

ACLs are defined using a DSL (domain specific language) that describes what a given user is allowed to do. Such rules are always implemented from the first to the last, left-to-right, because sometimes the order of the rules is important to understand what the user is really able to do.

By default there is a single user defined, called default. We can use the ACL LIST command in order to check the currently active ACLs and verify what the configuration of a freshly started, defaults-configured Redis instance is:

> ACL LIST
1) "user default on nopass ~* &* +@all"

The command above reports the list of users in the same format that is used in the Redis configuration files, by translating the current ACLs set for the users back into their description.

The first two words in each line are "user" followed by the username. The next words are ACL rules that describe different things. We'll show how the rules work in detail, but for now it is enough to say that the default user is configured to be active (on), to require no password (nopass), to access every possible key (~*) and Pub/Sub channel (&*), and be able to call every possible command (+@all).

Also, in the special case of the default user, having the nopass rule means that new connections are automatically authenticated with the default user without any explicit AUTH call needed.

ACL rules

The following is the list of valid ACL rules. Certain rules are just single words that are used in order to activate or remove a flag, or to perform a given change to the user ACL. Other rules are char prefixes that are concatenated with command or category names, key patterns, and so forth.

Enable and disallow users:

on: Enable the user: it is possible to authenticate as this user.
off: Disallow the user: it's no longer possible to authenticate with this user; however, previously authenticated connections will still work. Note that if the default user is flagged as off, new connections will start as not authenticated and will require the user to send AUTH or HELLO with the AUTH option in order to authenticate in some way, regardless of the default user configuration.

Allow and disallow commands:

+<command>: Add the command to the list of commands the user can call. Can be used with | for allowing subcommands (e.g "+config|get").
-<command>: Remove the command to the list of commands the user can call. Starting Redis 7.0, it can be used with | for blocking subcommands (e.g "-config|set").
+@<category>: Add all the commands in such category to be called by the user, with valid categories being like @admin, @set, @sortedset, ... and so forth, see the full list by calling the ACL CAT command. The special category @all means all the commands, both the ones currently present in the server, and the ones that will be loaded in the future via modules.
-@<category>: Like +@<category> but removes the commands from the list of commands the client can call.
+<command>|first-arg: Allow a specific first argument of an otherwise disabled command. It is only supported on commands with no sub-commands, and is not allowed as negative form like -SELECT|1, only additive starting with "+". This feature is deprecated and may be removed in the future.
allcommands: Alias for +@all. Note that it implies the ability to execute all the future commands loaded via the modules system.
nocommands: Alias for -@all.

Allow and disallow certain keys and key permissions:

~<pattern>: Add a pattern of keys that can be mentioned as part of commands. For instance ~* allows all the keys. The pattern is a glob-style pattern like the one of KEYS. It is possible to specify multiple patterns.
%R~<pattern>: (Available in Redis 7.0 and later) Add the specified read key pattern. This behaves similar to the regular key pattern but only grants permission to read from keys that match the given pattern. See key permissions for more information.
%W~<pattern>: (Available in Redis 7.0 and later) Add the specified write key pattern. This behaves similar to the regular key pattern but only grants permission to write to keys that match the given pattern. See key permissions for more information.
%RW~<pattern>: (Available in Redis 7.0 and later) Alias for ~<pattern>.
allkeys: Alias for ~*.
resetkeys: Flush the list of allowed keys patterns. For instance the ACL ~foo:* ~bar:* resetkeys ~objects:*, will only allow the client to access keys that match the pattern objects:*.

Allow and disallow Pub/Sub channels:

&<pattern>: (Available in Redis 6.2 and later) Add a glob style pattern of Pub/Sub channels that can be accessed by the user. It is possible to specify multiple channel patterns. Note that pattern matching is done only for channels mentioned by PUBLISH and SUBSCRIBE, whereas PSUBSCRIBE requires a literal match between its channel patterns and those allowed for user.
allchannels: Alias for &* that allows the user to access all Pub/Sub channels.
resetchannels: Flush the list of allowed channel patterns and disconnect the user's Pub/Sub clients if these are no longer able to access their respective channels and/or channel patterns.

Configure valid passwords for the user:

><password>: Add this password to the list of valid passwords for the user. For example >mypass will add "mypass" to the list of valid passwords. This directive clears the nopass flag (see later). Every user can have any number of passwords.
<<password>: Remove this password from the list of valid passwords. Emits an error in case the password you are trying to remove is actually not set.
#<hash>: Add this SHA-256 hash value to the list of valid passwords for the user. This hash value will be compared to the hash of a password entered for an ACL user. This allows users to store hashes in the acl.conf file rather than storing cleartext passwords. Only SHA-256 hash values are accepted as the password hash must be 64 characters and only contain lowercase hexadecimal characters.
!<hash>: Remove this hash value from the list of valid passwords. This is useful when you do not know the password specified by the hash value but would like to remove the password from the user.
nopass: All the set passwords of the user are removed, and the user is flagged as requiring no password: it means that every password will work against this user. If this directive is used for the default user, every new connection will be immediately authenticated with the default user without any explicit AUTH command required. Note that the resetpass directive will clear this condition.
resetpass: Flushes the list of allowed passwords and removes the nopass status. After resetpass, the user has no associated passwords and there is no way to authenticate without adding some password (or setting it as nopass later).

Note: if a user is not flagged with nopass and has no list of valid passwords, that user is effectively impossible to use because there will be no way to log in as that user.

Configure selectors for the user:

(<rule list>): (Available in Redis 7.0 and later) Create a new selector to match rules against. Selectors are evaluated after the user permissions, and are evaluated according to the order they are defined. If a command matches either the user permissions or any selector, it is allowed. See selectors for more information.
clearselectors: (Available in Redis 7.0 and later) Delete all of the selectors attached to the user.

Reset the user:

reset Performs the following actions: resetpass, resetkeys, resetchannels, off, -@all. The user returns to the same state it had immediately after its creation.

Create and edit user ACLs with the ACL SETUSER command

Users can be created and modified in two main ways:

Using the ACL command and its ACL SETUSER subcommand.
Modifying the server configuration, where users can be defined, and restarting the server. With an external ACL file, just call ACL LOAD.

In this section we'll learn how to define users using the ACL command. With such knowledge, it will be trivial to do the same things via the configuration files. Defining users in the configuration deserves its own section and will be discussed later separately.

To start, try the simplest ACL SETUSER command call:

> ACL SETUSER alice
OK

The ACL SETUSER command takes the username and a list of ACL rules to apply to the user. However the above example did not specify any rule at all. This will just create the user if it did not exist, using the defaults for new users. If the user already exists, the command above will do nothing at all.

Check the default user status:

> ACL LIST
1) "user alice off &* -@all"
2) "user default on nopass ~* ~& +@all"

The new user "alice" is:

In the off status, so AUTH will not work for the user "alice".
The user also has no passwords set.
Cannot access any command. Note that the user is created by default without the ability to access any command, so the -@all in the output above could be omitted; however, ACL LIST attempts to be explicit rather than implicit.
There are no key patterns that the user can access.
The user can access all Pub/Sub channels.

New users are created with restrictive permissions by default. Starting with Redis 6.2, ACL provides Pub/Sub channels access management as well. To ensure backward compatibility with version 6.0 when upgrading to Redis 6.2, new users are granted the 'allchannels' permission by default. The default can be set to resetchannels via the acl-pubsub-default configuration directive.

From 7.0, The acl-pubsub-default value is set to resetchannels to restrict the channels access by default to provide better security. The default can be set to allchannels via the acl-pubsub-default configuration directive to be compatible with previous versions.

Such user is completely useless. Let's try to define the user so that it is active, has a password, and can access with only the GET command to key names starting with the string "cached:".

> ACL SETUSER alice on >p1pp0 ~cached:* +get
OK

Now the user can do something, but will refuse to do other things:

> AUTH alice p1pp0
OK
> GET foo
(error) NOPERM this user has no permissions to access one of the keys used as arguments
> GET cached:1234
(nil)
> SET cached:1234 zap
(error) NOPERM this user has no permissions to run the 'set' command

Things are working as expected. In order to inspect the configuration of the user alice (remember that user names are case sensitive), it is possible to use an alternative to ACL LIST which is designed to be more suitable for computers to read, while ACL LIST is more human readable.

> ACL GETUSER alice
1) "flags"
2) 1) "on"
   2) "allchannels"
3) "passwords"
4) 1) "2d9c75..."
5) "commands"
6) "-@all +get"
7) "keys"
8) "~cached:*"
9) "channels"
10) "&*"
11) "selectors"
12) 1) 1) "commands"
       2) "-@all +set"
       3) "keys"
       4) "~*"
       5) "channels"
       6) "&*"

The ACL GETUSER returns a field-value array that describes the user in more parsable terms. The output includes the set of flags, a list of key patterns, passwords, and so forth. The output is probably more readable if we use RESP3, so that it is returned as a map reply:

> ACL GETUSER alice
1# "flags" => 1~ "on"
   2~ "allchannels"
2# "passwords" => 1) "2d9c75273d72b32df726fb545c8a4edc719f0a95a6fd993950b10c474ad9c927"
3# "commands" => "-@all +get"
4# "keys" => "~cached:*"
5# "channels" => "&*"
6# "selectors" => 1) 1# "commands" => "-@all +set"
    2# "keys" => "~*"
    3# "channels" => "&*"

Note: from now on, we'll continue using the Redis default protocol, version 2

Using another ACL SETUSER command (from a different user, because alice cannot run the ACL command), we can add multiple patterns to the user:

> ACL SETUSER alice ~objects:* ~items:* ~public:*
OK
> ACL LIST
1) "user alice on >2d9c75... ~cached:* ~objects:* ~items:* ~public:* &* -@all +get"
2) "user default on nopass ~* &* +@all"

The user representation in memory is now as we expect it to be.

Multiple calls to ACL SETUSER

It is very important to understand what happens when ACL SETUSER is called multiple times. What is critical to know is that every ACL SETUSER call will NOT reset the user, but will just apply the ACL rules to the existing user. The user is reset only if it was not known before. In that case, a brand new user is created with zeroed-ACLs. The user cannot do anything, is disallowed, has no passwords, and so forth. This is the best default for safety.

However later calls will just modify the user incrementally. For instance, the following sequence:

> ACL SETUSER myuser +set
OK
> ACL SETUSER myuser +get
OK

Will result in myuser being able to call both GET and SET:

> ACL LIST
1) "user default on nopass ~* &* +@all"
2) "user myuser off &* -@all +set +get"

Command categories

Setting user ACLs by specifying all the commands one after the other is really annoying, so instead we do things like this:

> ACL SETUSER antirez on +@all -@dangerous >42a979... ~*

By saying +@all and -@dangerous, we included all the commands and later removed all the commands that are tagged as dangerous inside the Redis command table. Note that command categories never include modules commands with the exception of +@all. If you say +@all, all the commands can be executed by the user, even future commands loaded via the modules system. However if you use the ACL rule +@read or any other, the modules commands are always excluded. This is very important because you should just trust the Redis internal command table. Modules may expose dangerous things and in the case of an ACL that is just additive, that is, in the form of +@all -... You should be absolutely sure that you'll never include what you did not mean to.

The following is a list of command categories and their meanings:

admin - Administrative commands. Normal applications will never need to use these. Includes REPLICAOF, CONFIG, DEBUG, SAVE, MONITOR, ACL, SHUTDOWN, etc.
bitmap - Data type: bitmaps related.
blocking - Potentially blocking the connection until released by another command.
connection - Commands affecting the connection or other connections. This includes AUTH, SELECT, COMMAND, CLIENT, ECHO, PING, etc.
dangerous - Potentially dangerous commands (each should be considered with care for various reasons). This includes FLUSHALL, MIGRATE, RESTORE, SORT, KEYS, CLIENT, DEBUG, INFO, CONFIG, SAVE, REPLICAOF, etc.
geo - Data type: geospatial indexes related.
hash - Data type: hashes related.
hyperloglog - Data type: hyperloglog related.
fast - Fast O(1) commands. May loop on the number of arguments, but not the number of elements in the key.
keyspace - Writing or reading from keys, databases, or their metadata in a type agnostic way. Includes DEL, RESTORE, DUMP, RENAME, EXISTS, DBSIZE, KEYS, EXPIRE, TTL, FLUSHALL, etc. Commands that may modify the keyspace, key, or metadata will also have the write category. Commands that only read the keyspace, key, or metadata will have the read category.
list - Data type: lists related.
pubsub - PubSub-related commands.
read - Reading from keys (values or metadata). Note that commands that don't interact with keys, will not have either read or write.
scripting - Scripting related.
set - Data type: sets related.
sortedset - Data type: sorted sets related.
slow - All commands that are not fast.
stream - Data type: streams related.
string - Data type: strings related.
transaction - WATCH / MULTI / EXEC related commands.
write - Writing to keys (values or metadata).

Redis can also show you a list of all categories and the exact commands each category includes using the Redis ACL command's CAT subcommand. It can be used in two forms:

ACL CAT -- Will just list all the categories available
ACL CAT <category-name> -- Will list all the commands inside the category

Examples:

 > ACL CAT
 1) "keyspace"
 2) "read"
 3) "write"
 4) "set"
 5) "sortedset"
 6) "list"
 7) "hash"
 8) "string"
 9) "bitmap"
10) "hyperloglog"
11) "geo"
12) "stream"
13) "pubsub"
14) "admin"
15) "fast"
16) "slow"
17) "blocking"
18) "dangerous"
19) "connection"
20) "transaction"
21) "scripting"

As you can see, so far there are 21 distinct categories. Now let's check what command is part of the geo category:

> ACL CAT geo
1) "geohash"
2) "georadius_ro"
3) "georadiusbymember"
4) "geopos"
5) "geoadd"
6) "georadiusbymember_ro"
7) "geodist"
8) "georadius"

Note that commands may be part of multiple categories. For example, an ACL rule like +@geo -@read will result in certain geo commands to be excluded because they are read-only commands.

Allow/block subcommands

Starting from Redis 7.0, subcommands can be allowed/blocked just like other commands (by using the separator | between the command and subcommand, for example: +config|get or -config|set)

That is true for all commands except DEBUG. In order to allow/block specific DEBUG subcommands, see the next section.

Allow the first-arg of a blocked command

Note: This feature is deprecated since Redis 7.0 and may be removed in the future.

Sometimes the ability to exclude or include a command or a subcommand as a whole is not enough. Many deployments may not be happy providing the ability to execute a SELECT for any DB, but may still want to be able to run SELECT 0.

In such case we could alter the ACL of a user in the following way:

ACL SETUSER myuser -select +select|0

First, remove the SELECT command and then add the allowed first-arg. Note that it is not possible to do the reverse since first-args can be only added, not excluded. It is safer to specify all the first-args that are valid for some user since it is possible that new first-args may be added in the future.

Another example:

ACL SETUSER myuser -debug +debug|digest

Note that first-arg matching may add some performance penalty; however, it is hard to measure even with synthetic benchmarks. The additional CPU cost is only paid when such commands are called, and not when other commands are called.

It is possible to use this mechanism in order to allow subcommands in Redis versions prior to 7.0 (see above section).

+@all VS -@all

In the previous section, it was observed how it is possible to define command ACLs based on adding/removing single commands.

Selectors

Starting with Redis 7.0, Redis supports adding multiple sets of rules that are evaluated independently of each other. These secondary sets of permissions are called selectors and added by wrapping a set of rules within parentheses. In order to execute a command, either the root permissions (rules defined outside of parenthesis) or any of the selectors (rules defined inside parenthesis) must match the given command. Internally, the root permissions are checked first followed by selectors in the order they were added.

For example, consider a user with the ACL rules +GET ~key1 (+SET ~key2). This user is able to execute GET key1 and SET key2 hello, but not GET key2 or SET key1 world.

Unlike the user's root permissions, selectors cannot be modified after they are added. Instead, selectors can be removed with the clearselectors keyword, which removes all of the added selectors. Note that clearselectors does not remove the root permissions.

Key permissions

Starting with Redis 7.0, key patterns can also be used to define how a command is able to touch a key. This is achieved through rules that define key permissions. The key permission rules take the form of %(<permission>)~<pattern>. Permissions are defined as individual characters that map to the following key permissions:

W (Write): The data stored within the key may be updated or deleted.
R (Read): User supplied data from the key is processed, copied or returned. Note that this does not include metadata such as size information (example STRLEN), type information (example TYPE) or information about whether a value exists within a collection (example SISMEMBER).

Permissions can be composed together by specifying multiple characters. Specifying the permission as 'RW' is considered full access and is analogous to just passing in ~<pattern>.

For a concrete example, consider a user with ACL rules +@all ~app1:* (+@readonly ~app2:*). This user has full access on app1:* and readonly access on app2:*. However, some commands support reading data from one key, doing some transformation, and storing it into another key. One such command is the COPY command, which copies the data from the source key into the destination key. The example set of ACL rules is unable to handle a request copying data from app2:user into app1:user, since neither the root permission or the selector fully matches the command. However, using key selectors you can define a set of ACL rules that can handle this request +@all ~app1:* %R~app2:*. The first pattern is able to match app1:user and the second pattern is able to match app2:user.

Which type of permission is required for a command is documented through key specifications. The type of permission is based off the keys logical operation flags. The insert, update, and delete flags map to the write key permission. The access flag maps to the read key permission. If the key has no logical operation flags, such as EXISTS, the user still needs either key read or key write permissions to execute the command.

Note: Side channels to accessing user data are ignored when it comes to evaluating whether read permissions are required to execute a command. This means that some write commands that return metadata about the modified key only require write permission on the key to execute: For example, consider the following two commands:

LPUSH key1 data: modifies "key1" but only returns metadata about it, the size of the list after the push, so the command only requires write permission on "key1" to execute.
LPOP key2: modifies "key2" but also returns data from it, the left most item in the list, so the command requires both read and write permission on "key2" to execute.

If an application needs to make sure no data is accessed from a key, including side channels, it's recommended to not provide any access to the key.

How passwords are stored internally

Redis internally stores passwords hashed with SHA256. If you set a password and check the output of ACL LIST or ACL GETUSER, you'll see a long hex string that looks pseudo random. Here is an example, because in the previous examples, for the sake of brevity, the long hex string was trimmed:

> ACL GETUSER default
1) "flags"
2) 1) "on"
   2) "allkeys"
   3) "allcommands"
   4) "allchannels"
3) "passwords"
4) 1) "2d9c75273d72b32df726fb545c8a4edc719f0a95a6fd993950b10c474ad9c927"
5) "commands"
6) "+@all"
7) "keys"
8) "~*"
9) "channels"
10) "&*"
11) "selectors"
12) (empty array)

Also, starting with Redis 6, the old command CONFIG GET requirepass will no longer return the clear text password, but instead the hashed password.

Using SHA256 provides the ability to avoid storing the password in clear text while still allowing for a very fast AUTH command, which is a very important feature of Redis and is coherent with what clients expect from Redis.

However ACL passwords are not really passwords. They are shared secrets between the server and the client, because the password is not an authentication token used by a human being. For instance:

There are no length limits, the password will just be memorized in some client software. There is no human that needs to recall a password in this context.
The ACL password does not protect any other thing. For example, it will never be the password for some email account.
Often when you are able to access the hashed password itself, by having full access to the Redis commands of a given server, or corrupting the system itself, you already have access to what the password is protecting: the Redis instance stability and the data it contains.

For this reason, slowing down the password authentication, in order to use an algorithm that uses time and space to make password cracking hard, is a very poor choice. What we suggest instead is to generate strong passwords, so that nobody will be able to crack it using a dictionary or a brute force attack even if they have the hash. To do so, there is a special ACL command ACL GENPASS that generates passwords using the system cryptographic pseudorandom generator:

> ACL GENPASS
"dd721260bfe1b3d9601e7fbab36de6d04e2e67b0ef1c53de59d45950db0dd3cc"

The command outputs a 32-byte (256-bit) pseudorandom string converted to a 64-byte alphanumerical string. This is long enough to avoid attacks and short enough to be easy to manage, cut & paste, store, and so forth. This is what you should use in order to generate Redis passwords.

Use an external ACL file

There are two ways to store users inside the Redis configuration:

Users can be specified directly inside the redis.conf file.
It is possible to specify an external ACL file.

The two methods are mutually incompatible, so Redis will ask you to use one or the other. Specifying users inside redis.conf is good for simple use cases. When there are multiple users to define, in a complex environment, we recommend you use the ACL file instead.

The format used inside redis.conf and in the external ACL file is exactly the same, so it is trivial to switch from one to the other, and is the following:

user <username> ... acl rules ...

For instance:

user worker +@list +@connection ~jobs:* on >ffa9203c493aa99

When you want to use an external ACL file, you are required to specify the configuration directive called aclfile, like this:

aclfile /etc/redis/users.acl

When you are just specifying a few users directly inside the redis.conf file, you can use CONFIG REWRITE in order to store the new user configuration inside the file by rewriting it.

The external ACL file however is more powerful. You can do the following:

Use ACL LOAD if you modified the ACL file manually and you want Redis to reload the new configuration. Note that this command is able to load the file only if all the users are correctly specified. Otherwise, an error is reported to the user, and the old configuration will remain valid.
Use ACL SAVE to save the current ACL configuration to the ACL file.

Note that CONFIG REWRITE does not also trigger ACL SAVE. When you use an ACL file, the configuration and the ACLs are handled separately.

ACL rules for Sentinel and Replicas

In case you don't want to provide Redis replicas and Redis Sentinel instances full access to your Redis instances, the following is the set of commands that must be allowed in order for everything to work correctly.

For Sentinel, allow the user to access the following commands both in the master and replica instances:

AUTH, CLIENT, SUBSCRIBE, SCRIPT, PUBLISH, PING, INFO, MULTI, SLAVEOF, CONFIG, CLIENT, EXEC.

Sentinel does not need to access any key in the database but does use Pub/Sub, so the ACL rule would be the following (note: AUTH is not needed since it is always allowed):

ACL SETUSER sentinel-user on >somepassword allchannels +multi +slaveof +ping +exec +subscribe +config|rewrite +role +publish +info +client|setname +client|kill +script|kill

Redis replicas require the following commands to be allowed on the master instance:

PSYNC, REPLCONF, PING

No keys need to be accessed, so this translates to the following rules:

ACL setuser replica-user on >somepassword +psync +replconf +ping

Note that you don't need to configure the replicas to allow the master to be able to execute any set of commands. The master is always authenticated as the root user from the point of view of replicas.

2 - TLS

Redis TLS support

SSL/TLS is supported by Redis starting with version 6 as an optional feature that needs to be enabled at compile time.

Getting Started

Building

To build with TLS support you'll need OpenSSL development libraries (e.g. libssl-dev on Debian/Ubuntu).

Run make BUILD_TLS=yes.

Tests

To run Redis test suite with TLS, you'll need TLS support for TCL (i.e. tcl-tls package on Debian/Ubuntu).

Run ./utils/gen-test-certs.sh to generate a root CA and a server certificate.
Run ./runtest --tls or ./runtest-cluster --tls to run Redis and Redis Cluster tests in TLS mode.

Running manually

To manually run a Redis server with TLS mode (assuming gen-test-certs.sh was invoked so sample certificates/keys are available):

./src/redis-server --tls-port 6379 --port 0 \
    --tls-cert-file ./tests/tls/redis.crt \
    --tls-key-file ./tests/tls/redis.key \
    --tls-ca-cert-file ./tests/tls/ca.crt

To connect to this Redis server with redis-cli:

./src/redis-cli --tls \
    --cert ./tests/tls/redis.crt \
    --key ./tests/tls/redis.key \
    --cacert ./tests/tls/ca.crt

Certificate configuration

In order to support TLS, Redis must be configured with a X.509 certificate and a private key. In addition, it is necessary to specify a CA certificate bundle file or path to be used as a trusted root when validating certificates. To support DH based ciphers, a DH params file can also be configured. For example:

tls-cert-file /path/to/redis.crt
tls-key-file /path/to/redis.key
tls-ca-cert-file /path/to/ca.crt
tls-dh-params-file /path/to/redis.dh

TLS listening port

The tls-port configuration directive enables accepting SSL/TLS connections on the specified port. This is in addition to listening on port for TCP connections, so it is possible to access Redis on different ports using TLS and non-TLS connections simultaneously.

You may specify port 0 to disable the non-TLS port completely. To enable only TLS on the default Redis port, use:

port 0
tls-port 6379

Client certificate authentication

By default, Redis uses mutual TLS and requires clients to authenticate with a valid certificate (authenticated against trusted root CAs specified by ca-cert-file or ca-cert-dir).

You may use tls-auth-clients no to disable client authentication.

Replication

A Redis master server handles connecting clients and replica servers in the same way, so the above tls-port and tls-auth-clients directives apply to replication links as well.

On the replica server side, it is necessary to specify tls-replication yes to use TLS for outgoing connections to the master.

Cluster

When Redis Cluster is used, use tls-cluster yes in order to enable TLS for the cluster bus and cross-node connections.

Sentinel

Sentinel inherits its networking configuration from the common Redis configuration, so all of the above applies to Sentinel as well.

When connecting to master servers, Sentinel will use the tls-replication directive to determine if a TLS or non-TLS connection is required.

In addition, the very same tls-replication directive will determine whether Sentinel's port, that accepts connections from other Sentinels, will support TLS as well. That is, Sentinel will be configured with tls-port if and only if tls-replication is enabled.

Additional configuration

Additional TLS configuration is available to control the choice of TLS protocol versions, ciphers and cipher suites, etc. Please consult the self documented redis.conf for more information.

Performance considerations

TLS adds a layer to the communication stack with overheads due to writing/reading to/from an SSL connection, encryption/decryption and integrity checks. Consequently, using TLS results in a decrease of the achievable throughput per Redis instance (for more information refer to this discussion).

Limitations

I/O threading is currently not supported with TLS.