In this instance with iOS 12.4, there was an internal misstep where important code was removed. With this update, phones can be jailbroken again and are now vulnerable to spyware or worse. The implications for this are far-reaching.
Photos, emails, phone numbers and possibly even banking data could be stolen if you installed an app that was able to exploit these escalated privileges. For those who want to have the flexibility that comes with a jailbroken phone, it’s critical that you’re educated on all the vulnerabilities and security issues this opens up for you.