Bob has accessed a nice site that sells high end wireless network equipment. However, after looking around for a while it was obvious that most items were too expensive for his low income salary…

Bob has accessed a nice site that sells high end wireless network equipment. However, after looking around for a while it was obvious that most items were too expensive for his low income salary. After fidding around for a while, he identified that modifying some of the page variables would allow him to modify the price easily and then he could save the page locally and resubmit the page in order to get a significant rebate. What weakness within the page code did he use to perform his attack?