This document provides an introduction to the topic of security from the point of view of Valkey. It covers the access control provided by Valkey, 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
Valkey is designed to be accessed by trusted clients inside trusted environments. This means that usually it is not a good idea to expose the Valkey instance directly to the internet or, in general, to an environment where untrusted clients can directly access the Valkey TCP port or UNIX socket.
For instance, in the common context of a web application implemented using Valkey as a database, cache, or messaging system, the clients inside the front-end (web side) of the application will query Valkey to generate pages or to perform operations requested or triggered by the web application user.
In this case, the web application mediates access between Valkey and untrusted clients (the user browsers accessing the web application).
In general, untrusted access to Valkey should always be mediated by a layer implementing ACLs, validating user input, and deciding what operations to perform against the Valkey instance.
Network security
Access to the Valkey port should be denied to everybody but trusted clients in the network, so the servers running Valkey should be directly accessible only by the computers implementing the application using Valkey.
In the common case of a single computer directly exposed to the internet, such as a virtualized Linux instance (Linode, EC2, ...), the Valkey port should be firewalled to prevent access from the outside. Clients will still be able to access Valkey using the loopback interface.
Note that it is possible to bind Valkey to a single interface by adding a line like the following to the valkey.conf file:
bind 127.0.0.1
Failing to protect the Valkey port from the outside can have a big security
impact because of the nature of Valkey. 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 Valkey instances from being accessed from external networks. Many instances are simply left exposed on the internet with public IPs. Valkey 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, Valkey 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 Valkey properly.
We expect protected mode to seriously decrease the security issues caused by unprotected Valkey instances executed without proper administration. However, the system administrator can still ignore the error given by Valkey and disable protected mode or manually bind all the interfaces.
Authentication
Valkey provides two ways to authenticate clients. The recommended authentication method is via Access Control Lists, allowing named users to be created and assigned fine-grained permissions. Read more about Access Control Lists here.
The legacy authentication method is enabled by editing the valkey.conf file, and providing a database password using the requirepass setting.
This password is then used by all clients.
When the requirepass setting is enabled, Valkey 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 valkey.conf file. It should be long enough to prevent brute force attacks for two reasons:
- Valkey is very fast at serving queries. Many passwords per second can be tested by an external client.
- The Valkey password is stored in the valkey.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 Valkey from external attackers fail, an external client will still not be able to access the Valkey instance without knowledge of the authentication password.
Since the AUTH command, like every other Valkey command, is sent unencrypted, it
does not protect against an attacker that has enough access to the network to
perform eavesdropping.
TLS support
Valkey has optional support for TLS on all communication channels, including client connections, replication links, and the Valkey Cluster bus protocol.
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 Valkey that triggers pathological (worst case) algorithm complexity on data structures implemented inside Valkey 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, Valkey uses a per-execution, pseudo-random seed to the hash function.
Valkey 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 Valkey 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
Internally, Valkey uses all the well-known practices for writing secure code to prevent buffer overflows, format bugs, and other memory corruption issues.
Valkey does not require root privileges to run. It is recommended to run it as an unprivileged valkey user that is only used for this purpose.