Just In Time (JIT) Image Manipulation
Image thumbnailer
New#1: Denial of Service Vulnerability
This should do it.
http://github.com/nickdunn/jit_image_manipulation/commit/91a8cd8f69eb67b24283cf7ee19a432f3498e2cd
And a description: http://getsymphony.com/discuss/thread/184/5/#position-95
Please, see this issue in the general issue tracker.