The SoapClient::__call method in ext/soap/soap.c in PHP before 5.4.39, 5.5.x before 5.5.23, and 5.6.x before 5.6.7 does not verify that __default_headers is an array, which allows remote attackers to execute arbitrary code by providing crafted serialized data with an unexpected data type, related to a type confusion issue. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-4147
