Hello aspirant,

Yes CBSE can fail a student if he gets less than what is required to pass, it also depends on the teacher who is checking your paper and not on CBSE, as the teacher who is checking, if he/she is liberal and understands that you would lose your entire year because of this might increase your few marks if they find something valuable in your answer  sheet, but if they fail to find anything worth giving marks and you have performed very poorly on the answer sheet than there is a very low chances that they will show some mercy and give you passing marks, while if any question in your paper was out of syllabus or exceptionally tough and if grace marks is allowed for that than there is  a chance they might give it but else there is very less chances that they will pass someone who is short of 4-5 marks to even pass.