The setRequestHeader method of the XMLHttpRequest object in Microsoft Internet Explorer 7 does not restrict the dangerous Transfer-Encoding HTTP request header, which allows remote attackers to conduct HTTP request splitting and HTTP request smuggling attacks via a POST containing a "Transfer-Encoding: chunked" header and a request body with an incorrect chunk size.
https://exchange.xforce.ibmcloud.com/vulnerabilities/42804
http://www.vupen.com/english/advisories/2008/0980
http://www.securityfocus.com/archive/1/489960/100/0/threaded