How does a Misuse Case relate to a regular Use Case in a diagram?

Question

Accepted Answer

A dashed arrow labelled "threatens" runs FROM the Misuse Case TO the use case it endangers — the attacker drives the MUC, the MUC threatens the UC.
The arrow always points from the dark (attack) oval into the white (legitimate) one it puts at risk:
User -----> [Use Case] <----threatens---- [Misuse Case] <----- Attacker
             (white)                         (black)

The three relationships, all pointing from the MUC outward:

Relationship
From
To
Meaning

threatens
Misuse Case
Use Case
The MUC endangers this UC (puts its security at risk)

exploits
Misuse Case
Use Case
The MUC abuses this specific UC as its way in

mitigates
Mitigation Case
Misuse Case
A control that cancels the MUC

threatens vs exploits — the subtle bit: an attack often exploits the UC that is its entry point but threatens a different UC that suffers the damage. In a login attack, an injection exploits "Enter username" (where the bad input goes in) yet threatens "Use system" (the protected functionality it ultimately compromises).

Relationship	From	To	Meaning
threatens	Misuse Case	Use Case	The MUC endangers this UC (puts its security at risk)
exploits	Misuse Case	Use Case	The MUC abuses this specific UC as its way in
mitigates	Mitigation Case	Misuse Case	A control that cancels the MUC