Upgrade PHP 7.3, 7.2 & 7.1 to current iterations.
Security vulnerability alerts for the following versions of PHP

PHP 7.1 versions prior to 7.1.32

PHP 7.2 versions prior to 7.2.22

PHP 7.3 versions prior to 7.3.9

As of today, There are currently no reports of these vulnerabilities being exploited in the wild.
Successfully exploiting the most severe of these vulnerabilities could allow for arbitrary code execution in the context of the affected application. Depending on the privileges associated with the application, an attacker could install programs; view, change, or delete data; or create new accounts with full user rights. Failed exploitation could result in a denial-of-service condition.
https://www.cisecurity.org/advisory/multiple-vulnerabilities-in-php-could-allow-for-arbitrary-code-execution_2019-087/