Improper Input Validation in multi_xml

multi_xml gem 0.5.2 for Ruby, as used in Grape before 0.2.6 and possibly other products, does not properly restrict casts of string values, which allows remote attackers to conduct object-injection attacks and execute arbitrary code, or cause a denial of service (memory and CPU consumption) involving nested XML entity references, by leveraging support for (1) YAML type conversion or (2) Symbol type conversion, a similar vulnerability to CVE-2013-0156.