lib/rexml/text.rb in the REXML parser in Ruby before 1.9.3-p392 allows remote attackers to cause a denial of service (memory consumption and crash) via crafted text nodes in an XML document, aka an XML Entity Expansion (XEE) attack.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.