A basic definition of a security bug is something that violates confidentiality, integrity or availability.
A DoS affects the availability of an application, and as such is a real security bug. While the severity of it might be lower than a bug that allows to "empty bank accounts", and fixing it might get a lower priority, it doesn't make it any less real.
A DoS affects the availability of an application, and as such is a real security bug. While the severity of it might be lower than a bug that allows to "empty bank accounts", and fixing it might get a lower priority, it doesn't make it any less real.