This is a very real and serious attack. The IV weakness of SSL looks very scary.

This MitM attack very feasible over wifi/corporate networks. For example, (simplifying a lot):

  * Initial shopping session example.com (HTTP)
  * User proceeds to payment stage payment.com
  * Browser with auth cookie for SSL payment.com
  * payment.com redirects to success page at example.com HTTP
  * Attacker MitM success page adding HTTP iframe to payment.com
  * Attacker serves fake iframe with JS code
  * The iframe has same-origin to payment.com
  * iframe does thousands of carefully crafted ajax/form requests to SSL payment.com
  * Optional 1: attacker snoops those requests/response to hint JS iframe
  * Optional 2: attacker blocks those requests
  * Since it's local MitM thousands of requests can be fired in seconds

The attacker could use specially crafted URLs at https://payment.com and headers using XMLHTTPRequest.setRequestHeader() for the known plaintext.