Symeon Paraschoudis discovered that the curl_easy_duphandle function in cURL, an URL transfer library, has a bug that can lead to libcurl eventually sending off sensitive data that was not intended for sending, while performing a HTTP POST operation. This bug requires CURLOPT_COPYPOSTFIELDS and curl_easy_duphandle to be used in that order, and then the duplicate handle must be used to perform the HTTP POST. The curl command line tool is not affected by this problem as it does not use this sequence.