ruby: REXML billion laughs attack via parameter entity expansion

The REXML parser in Ruby 1.9.x before 1.9.3-p550, 2.0.x before 2.0.0-p594, and 2.1.x before 2.1.4 allows remote attackers to cause a denial of service memory consumption via a crafted XML document, aka an XML Entity Expansion XEE attack...