In PHP 7.x before 7.0.21 and 7.1.x before 7.1.7, ext/intl/msgformat/msgformat_parse.c does not restrict the locale length, which allows remote attackers to cause a denial of service (stack-based buffer overflow and application crash) or possibly have unspecified other impact within International Components for Unicode (ICU) for C/C++ via a long first argument to the msgfmt_parse_message function.