This indicates an attack attempt to exploit an Remote Command Injection vulnerability in CraftCMS plugin SEOmatic.
The vulnerability is due to insufficient sanitizing of user-supplied input. An attacker can exploit this issue to inject arbitrary code, which will be executed in the target user's system.
CraftCMS plugin SEOmatic before 3.3.0
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.