Modbus port is not getting responded when there is an http request with malformed URL.

The remote web server does not respond after it receives a URL consisting of a long string of '%' characters (refer Nessus Plugin ID 11155).
After system recieves the malformed URL with long string of '%' character, the callback function corresponding to modbus data recieve is not invoked.
As per my analysis I doubt when URL with long string of '%' character comes as http GET request the memory space corresponds to tcp_info structure for modbus port is getting overwritten.
How to resolve this issue?.
I believe if we add some bound check for number of characters in URL this can be resolved. Where to add a bound check to number of characters in URL?.
Also how to increase the maximum size of URL?.

Environment Details :
MCU - LPC2468
IDE - Keil Microvision-4
TCP stack used - TCP_ARM_L.LIB

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