Strictly speaking you are right, but people commonly use "illegal" as "in violation of international treaties". Since there's no super-national sovereign to enf

Strictly speaking you are right, but people commonly use "illegal" as "in violation of international treaties". Since there's no super-national sovereign to enforce those, it's not the same sort of illegal as we usually mean, but it is functionally close. That said, from what I understand, ccTLDs are owned by countries they are allocated to (maybe with some corner cases, but irrelevant here), so Mali is certainly not doing anything wrong even in the above "legal" sense by asserting their ownership.