The regular expression engine in JRuby before 1.4.1, when $KCODE is set to 'u', does not properly handle characters immediately after a UTF-8 character, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted string.
https://exchange.xforce.ibmcloud.com/vulnerabilities/80277
https://bugzilla.redhat.com/show_bug.cgi?id=750306
https://bugs.gentoo.org/show_bug.cgi?id=317435