Front end limits the length of the input values

5 chars max:        

Step 1: Try to fill in 5+ chars. Click "submit"

Step 2: After clicking "submit", the result shows. Then, modify the URL in the address bar to ".../php/2.php?d1=1234567890", which is a crafted request.


Front end limits the content of the input values

The input should not contain "ab":        

Step 1: Type in a string that contains "ab", click "submit".

Step 2: Type in a string that doesn't contain "ab", click "submit". Then, in the result page, modify the URL in the address bar to ".../php/2.php?d2=ab" and send the request.


Front end limits the combination of the input values

Either "OS" or "Algorithm" should be selected, but not both:

OS
Algorithm

   

Step 1: Select "OS" and "Algorithm" together. Click "submit".

Step 2: Deselect both. Click "submit".

Step 3: Select either of them. Click "submit". Then, in the result page, modify the URL in the address bar to ".../php/2.php?op1=OS&op2=Algorithm" and send the request.