The neat thing about the log4j thing was even a cursory explanation of the vulnerability made anyone with a passing familiarity with security say, "Why the fuck would that even be a feature?!"
Basically it involved parsing JNDI stuff which involved grabbing remote code (but that was a niche feature of JNDI in the Dev's defense). Basically, you may think it is just something like variable substitution but can involve much crazier stuff