An issue was discovered in PHP 7.3.x before 7.3.1. An invalid multibyte string supplied as an argument to the mb_split() function in ext/mbstring/php_mbregex.c can cause PHP to execute memcpy() with a negative argument, which could read and write past buffers allocated for the data.
CREATE(Triage): {Link=https://nvd.nist.gov/vuln/detail/CVE-2019-9025 User=admin}
