The compile_bracket_matchingpath function in pcre_jit_compile.c in PCRE through 8.x before revision 1680 (e.g., the PHP 7.1.1 bundled version) allows remote attackers to cause a denial of service (out-of-bounds read and application crash) via a crafted regular expression.
https://vcs.pcre.org/pcre/code/trunk/pcre_jit_compile.c?r1=1676&r2=1680&view=patch
https://security.gentoo.org/glsa/201706-11
https://bugs.exim.org/show_bug.cgi?id=2035
https://access.redhat.com/errata/RHSA-2018:2486