Colleges have been aware of the problem with forged transcripts from overseas for several decades by now. This is nothing new to them.
If you feel that this will harm your own chances, send an anonymous communication to the colleges that you have applied to, stating that a valid transcript from your school would be on school letterhead, in such and such a format, and that you have become aware that there has been an incident of a forged transcript from your school this year.
The school should have expelled the perpetrator, and informed the colleges that the perpetrator had applied to. Clearly, the school itself has questionable values, since it is more concerned with hiding wrongdoing and protecting its reputation, than in cleaning house and correcting the wrongdoing. Unfortunately, in some countries this behavior permeates the society, from the top down. If you do something, you’d better do it anonymously, because if the school were to find out that you had “outed” them to the colleges, YOU could wind up being the one expelled.