Redis is an in-memory database that persists on disk. By exploiting weaknesses in the Lua script execution environment, an attacker with access to Redis prior to version 7.0.0 or 6.2.7 can inject Lua code that will execute with the (potentially higher) privileges of another Redis user. The Lua script execution environment in Redis provides some measures that prevent a script from creating side effects that persist and can affect the execution of the same, or different script, at a later time. Several weaknesses of these measures have been publicly known for a long time, but they had no security impact as the Redis security model did not endorse the concept of users or privileges. With the introduction of ACLs in Redis 6.0, these weaknesses can be exploited by a less privileged users to inject Lua code that will execute at a later time, when a privileged user executes a Lua script. The problem is fixed in Redis versions 7.0.0 and 6.2.7. An additional workaround to mitigate this problem without patching the redis-server executable, if Lua scripting is not being used, is to block access to `SCRIPT LOAD` and `EVAL` commands using ACL rules.

References:

https://github.com/redis/redis/pull/10651
https://github.com/redis/redis/security/advisories/GHSA-647m-2wmq-qmvq
https://github.com/redis/redis/releases/tag/7.0.0
https://github.com/redis/redis/releases/tag/6.2.7