Passport validity
The source states no minimum passport validity.
Visa rules · Tourist entry
Entry rules for the Cocos (Keeling) Islands from its official sources, and every passport we have a page for.
Normal Australian immigration procedures apply when you arrive on the Cocos (Keeling) Islands from outside Australia, and you may need a visa.
Official sources
The source states no minimum passport validity.
Pick your passport for the full rule, its source quote and the check date.