A local or remote attacker can execute programs with root privileges - if you've an unusual configuration.
If your configuration uses the ${sort } expansion for items that can be controlled by an attacker (e.g. $local_part, $domain). The default config, as shipped by the Exim developers, does not contain ${sort }.
The vulnerability is exploitable either remotely or locally and could
be used to execute other programs with root privilege. The ${sort }
expansion re-evaluates its items.
Exim 4.92.1 is not vulnerable.