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.