This release brings a security fix for JSON::Pure::Parser. Quoting json's CHANGELOG:

A specially designed string could
cause catastrophic backtracking in one of the parser's regular expressions
in earlier 1.1.x versions. JSON::Ext::Parser isn't affected by this issue.
Thanks to Bartosz Blimke <bartosz@new-bamboo.co.uk> for reporting this
problem.

To install/update, simply perform:

jruby -S gem install json-jruby