My brother scored 428 in 2015, and he was qualified for the CSE branch, but instead, he chose ME. In the current situation, a score of more than 440 is required to obtain a spot in CSE.

Because the cut-off for each year varies, it's difficult to specify what the minimum marks are required for CSE.

You can check the cut-off stats for CSE in the last few years in the table below. 

Hope this gives you some idea about the cutoff required for CSE at IET Lucknow.