When an interrupt transfers control to an operating system, a Kernel stack area separate from the stack of the interrupted process is generally used. Why?

Control is transmitted to the operating system when an interrupt happens, which determines what action is to be done to be taken or usually what interrupt services.

If the kernel leaves data in the memory space of a user program when returning from a system call, it may be possible for a malicious user to use this data to find out about other processes. In these systems, the kernel synchronizes by preventing interrupts in critical sections with interrupt handlers on a processor. Operating system may crash if it controls the interrupts because a poorly written user program does not provide sufficient stacking room.