Long vacations kill production

It was a suprise when I worked with an HR platform project. The project was in production for years, leave requests were a critical feature for the company. When new leave request are submitted, we will create a lot of background jobs to create calendar events, send emails, and notify managers, records for reportings, etc.

In a beautiful day, all servers are down because an user accidently submitted a leave request for 100 years. There is no validation for the leave request duration.

The fix is pretty easy but the scenario is interesting. Who will submmit a leave requets for 100 years?