Oniguruma through 6.9.3, as used in PHP 7.3.x and other products, has a heap-based buffer over-read in str_lower_case_match in regexec.c.
https://usn.ubuntu.com/4460-1/
https://lists.debian.org/debian-lts-announce/2019/12/msg00002.html
https://github.com/kkos/oniguruma/commit/d3e402928b6eb3327f8f7d59a9edfa622fec557b