Adobe Flash Player before 9.0.277.0 and 10.x before 10.1.53.64, and Adobe AIR before 2.0.2.12610, allows remote web servers to cause a denial of service (NULL pointer dereference and browser crash) by returning a different response when an HTTP request is sent a second time, as demonstrated by two responses that provide SWF files with different SWF version numbers.
CWE-399