Recently several serious bugs were fixed in Oniguruma,
CVE-2017-{9224,9225,9226,9227,9228,9229}:

https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=oniguruma
https://github.com/kkos/oniguruma#fixed-security-issues

I'm not sure exactly which Oniguruma release fixed the bugs.

Ruby includes vulnerable code from Oniguruma. I didn't see any fixes in
the Ruby Git repo.

I tried building PHP with Oniguruma 6.4.0 or 6.5.0 but the PHP test
suite fails like this:

=====================================================================
FAILED TEST SUMMARY
---------------------------------------------------------------------
Bug #72994 (mbc_to_code() out of bounds read) [ext/mbstring/tests/bug72994.phpt]
Test mb_ereg_replace() function : usage variations  - <type here specifics of this variation> [ext/mbstring/tests/mb_ereg_replace_variation1.phpt]
Test mb_ereg() function : usage variations - pass different character classes to see they match correctly [ext/mbstring/tests/mb_ereg_variation3.phpt]
=====================================================================

I tried using the bundled Oniguruma, which includes the fixes, and it
fails like this:

=====================================================================
FAILED TEST SUMMARY
---------------------------------------------------------------------
Bug #60120 proc_open hangs with stdin/out with 2048+ bytes [ext/standard/tests/streams/proc_open_bug60120.phpt]
=====================================================================