These words can be characterized by two facets:
- effect of the spell
- intention of the spell-caster
Lets deal with 呪縛 first by looking at its two Kanjis:
- 呪: spell, curse
- 縛: to truss, to bind
So 呪縛される literally means to be restricted by a spell.
- effect: partially or wholly restrict someone's movement or thought
- intention: mostly bad, sometimes good depending on the context (or neutral if you're bound by a past event.)
忍者が呪縛の術をとなえた。A ninja cast a spell of paralysis. [effect: paralysis][intention: good if you're an ally of the ninja, bad for the enemy]
過去の呪縛にとらわれる。Fettered by the past. [effect: restriction of thought][intention: neutral]
呪う translates directly to "curse".
- effect: something bad, like bad fortune or death.
- intention: bad
末代まで呪ってやる! I curse you forever!
Note that nothing may happen even if you were 呪われた by someone. Anything can happen in between the act of cursing and the effect to take place. On the contrary, 呪縛された means you're already bound by a spell.
Also, 呪い can have an on/off state; you can "be under a 呪い"(呪いがかかっている), "break a 呪い"(呪いをとく). This is similar to 呪縛: you can "be under a 呪縛"(呪縛にかかっている), "break a 呪縛"(呪縛をとく). The difference is that 呪縛 has a constant effect on the victim, while 呪い takes effect in a (series of) short event(s) (though it depends largely on the content of the curse).